diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -2,6 +2,10 @@
 
 `tmp-proc` uses [PVP Versioning][1].
 
+## 0.6.0.0 -- 2024-01-09
+
+* Removed SomeProcs
+
 ## 0.5.3.0 -- 2023-08-11
 
 * Add HList constructors `only` and `both` (alias: `&:&`)
diff --git a/src/System/TmpProc/Docker.hs b/src/System/TmpProc/Docker.hs
--- a/src/System/TmpProc/Docker.hs
+++ b/src/System/TmpProc/Docker.hs
@@ -52,13 +52,15 @@
     Proc (..)
   , Pinged (..)
   , AreProcs
-  , SomeProcs (..)
   , nameOf
   , startup
   , toPinged
   , uriOf'
   , runArgs'
 
+    -- * @'ToRunCmd'@
+  , ToRunCmd (..)
+
     -- * @'ProcHandle'@
   , ProcHandle (..)
   , Proc2Handle
@@ -110,6 +112,7 @@
 import qualified Data.ByteString.Char8 as C8
 import Data.Kind (Type)
 import Data.List (dropWhileEnd)
+import Data.Maybe (isJust)
 import Data.Proxy (Proxy (..))
 import Data.Text (Text)
 import qualified Data.Text as Text
@@ -196,11 +199,12 @@
 startupAll :: AreProcs procs => HList procs -> IO (HandlesOf procs)
 startupAll = go procProof
   where
-    go :: SomeProcs as -> HList as -> IO (HandlesOf as)
-    go SomeProcsNil HNil = pure HNil
-    go (SomeProcsCons cons) (x `HCons` y) = do
-      h <- startup x
-      others <- go cons y `onException` terminate h
+    go :: Uniquely Proc AreProcs as -> HList as -> IO (HandlesOf as)
+    go UniquelyNil HNil = pure HNil
+    go (UniquelyCons cons) (x `HCons` y) = do
+      others <- go cons y
+      h <- startup x `onException` terminateAll others
+      -- others <- go cons y `onException` terminate h
       pure $ h `HCons` others
 
 
@@ -223,6 +227,23 @@
   void $ readProcess "docker" ["rm", pid] ""
 
 
+{- | Allow customization of the docker command that launches a @'Proc'@
+|
+| The full command is
+|   `docker run -d <optional-args> $(imageText a)`
+|
+| A fallback instance is provided that works for any instance of @Proc a@
+| Specify a new instance of @ToRunCmd@ to control <optional-args>
+-}
+class ToRunCmd a where
+  -- * Generate args that follow the initial ['docker', 'run', '-d']
+  toRunCmd :: a -> [Text]
+
+
+instance {-# OVERLAPPABLE #-} (Proc a) => ToRunCmd a where
+  toRunCmd _ = runArgs @a
+
+
 -- | Specifies how to a get a connection to a 'Proc'.
 class Proc a => Connectable a where
   -- | The connection type.
@@ -322,13 +343,8 @@
 
 
 -- | The full args of a @docker run@ command for starting up a 'Proc'.
-dockerCmdArgs :: forall a. (Proc a) => [Text]
-dockerCmdArgs =
-  [ "run"
-  , "-d"
-  ]
-    <> runArgs @a
-    <> [imageText' @a]
+dockerCmdArgs :: forall a. (Proc a, ToRunCmd a) => a -> [Text]
+dockerCmdArgs x = ["run", "-d"] <> toRunCmd x <> [imageText' @a]
 
 
 imageText' :: forall a. (Proc a) => Text
@@ -350,12 +366,12 @@
 
 Returns the 'ProcHandle' used to control the 'Proc' once a ping has succeeded.
 -}
-startup :: forall a. Proc a => a -> IO (ProcHandle a)
+startup :: (Proc a, ToRunCmd a) => a -> IO (ProcHandle a)
 startup x = do
-  let fullArgs = dockerCmdArgs @a
+  let fullArgs = map Text.unpack $ dockerCmdArgs x
       isGarbage = flip elem ['\'', '\n']
       trim = dropWhileEnd isGarbage . dropWhile isGarbage
-  runCmd <- dockerRun (map Text.unpack fullArgs)
+  runCmd <- dockerRun fullArgs
   hPid <- trim <$> readCreateProcess runCmd ""
   hAddr <-
     Text.pack . trim
@@ -367,8 +383,7 @@
         , "'{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}'"
         ]
         ""
-  let hUri = uriOf @a hAddr
-      h = ProcHandle {hProc = x, hPid, hUri, hAddr}
+  let h = ProcHandle {hProc = x, hPid, hUri = uriOf' x hAddr, hAddr}
   (nPings h `onException` terminate h) >>= \case
     OK -> pure h
     pinged -> do
@@ -604,23 +619,24 @@
   Handle2KV (ProcHandle t ': ts) = KV (Name t) (ProcHandle t) ': Handle2KV ts
 
 
--- | Used by @'AreProcs'@ to prove a list of types just contains @'Proc's@.
-data SomeProcs (as :: [Type]) where
-  SomeProcsNil :: SomeProcs '[]
-  SomeProcsCons :: (Proc a, IsAbsent a as) => SomeProcs as -> SomeProcs (a ': as)
-
-
 -- | Declares a proof that a list of types only contains @'Proc's@.
 class AreProcs as where
-  procProof :: SomeProcs as
+  procProof :: Uniquely Proc AreProcs as
 
 
 instance AreProcs '[] where
-  procProof = SomeProcsNil
+  procProof = UniquelyNil
 
 
-instance (Proc a, AreProcs as, IsAbsent a as) => AreProcs (a ': as) where
-  procProof = SomeProcsCons procProof
+instance
+  ( Proc a
+  , ToRunCmd a
+  , AreProcs as
+  , IsAbsent a as
+  ) =>
+  AreProcs (a ': as)
+  where
+  procProof = UniquelyCons procProof
 
 
 -- | Used to prove a list of types just contains @'ProcHandle's@.
@@ -629,28 +645,22 @@
   SomeHandlesCons :: Proc a => SomeHandles as -> SomeHandles (ProcHandle a ': as)
 
 
-p2h :: SomeProcs as -> SomeHandles (Proc2Handle as)
-p2h SomeProcsNil = SomeHandlesNil
-p2h (SomeProcsCons cons) = SomeHandlesCons (p2h cons)
-
-
--- | Used by @'Connectables'@ to prove a list of types just contains @'Connectable's@.
-data SomeConns (as :: [Type]) where
-  SomeConnsNil :: SomeConns '[]
-  SomeConnsCons :: (Connectable a, IsAbsent a as) => SomeConns as -> SomeConns (a ': as)
+p2h :: Uniquely Proc AreProcs as -> SomeHandles (Proc2Handle as)
+p2h UniquelyNil = SomeHandlesNil
+p2h (UniquelyCons cons) = SomeHandlesCons (p2h cons)
 
 
 -- | Declares a proof that a list of types only contains @'Connectable's@.
 class Connectables as where
-  connProof :: SomeConns as
+  connProof :: Uniquely Connectable Connectables as
 
 
 instance Connectables '[] where
-  connProof = SomeConnsNil
+  connProof = UniquelyNil
 
 
 instance (Connectable a, Connectables as, IsAbsent a as) => Connectables (a ': as) where
-  connProof = SomeConnsCons connProof
+  connProof = UniquelyCons connProof
 
 
 -- | Convert list of 'Connectable' types to corresponding 'Conn' types.
@@ -663,9 +673,9 @@
 openAll :: Connectables xs => HandlesOf xs -> IO (HList (ConnsOf xs))
 openAll = go connProof
   where
-    go :: SomeConns as -> HandlesOf as -> IO (HList (ConnsOf as))
-    go SomeConnsNil HNil = pure HNil
-    go (SomeConnsCons cons) (x `HCons` y) = do
+    go :: Uniquely Connectable Connectables as -> HandlesOf as -> IO (HList (ConnsOf as))
+    go UniquelyNil HNil = pure HNil
+    go (UniquelyCons cons) (x `HCons` y) = do
       c <- openConn x
       others <- go cons y `onException` closeConn c
       pure $ c `HCons` others
@@ -675,9 +685,9 @@
 closeAll :: Connectables procs => HList (ConnsOf procs) -> IO ()
 closeAll = go connProof
   where
-    go :: SomeConns as -> HList (ConnsOf as) -> IO ()
-    go SomeConnsNil HNil = pure ()
-    go (SomeConnsCons cons) (x `HCons` y) = closeConn x >> go cons y
+    go :: Uniquely Connectable Connectables as -> HList (ConnsOf as) -> IO ()
+    go UniquelyNil HNil = pure ()
+    go (UniquelyCons cons) (x `HCons` y) = closeConn x >> go cons y
 
 
 -- | Open some connections, use them in an action; close them.
@@ -713,6 +723,14 @@
 withNamedConns proxy = withConns . manyNamed proxy
 
 
+{- | Used to support type classes that prove a list of types is constrained to
+unique instances of another type class.
+-}
+data Uniquely f fs (as :: [Type]) where
+  UniquelyNil :: Uniquely f fs '[]
+  UniquelyCons :: (IsAbsent a as, f a, fs as) => Uniquely f fs as -> Uniquely f fs (a ': as)
+
+
 sortHandles ::
   ( handles ~ Proc2Handle ps
   , sorted ~ SortHandles handles
@@ -770,7 +788,7 @@
 
 
 showDebug :: IO Bool
-showDebug = fmap (maybe False (const True)) $ lookupEnv debugEnv
+showDebug = isJust <$> lookupEnv debugEnv
 
 
 debugEnv :: String
diff --git a/test/Test/HttpBin.hs b/test/Test/HttpBin.hs
--- a/test/Test/HttpBin.hs
+++ b/test/Test/HttpBin.hs
@@ -19,6 +19,7 @@
   , Proc (..)
   , ProcHandle (..)
   , SvcURI
+  , ToRunCmd (..)
   , manyNamed
   , startupAll
   , toPinged
@@ -43,6 +44,10 @@
   runArgs = []
   reset _ = pure ()
   ping = ping'
+
+
+instance ToRunCmd NginxTest where
+  toRunCmd _ = []
 
 
 -- | A data type representing a connection to a HttpBin server.
diff --git a/tmp-proc.cabal b/tmp-proc.cabal
--- a/tmp-proc.cabal
+++ b/tmp-proc.cabal
@@ -1,6 +1,6 @@
 cabal-version:      3.0
 name:               tmp-proc
-version:            0.5.3.0
+version:            0.6.0.0
 synopsis:           Run 'tmp' processes in integration tests
 description:
   @tmp-proc@ runs services in docker containers for use in integration tests.