I pit all my goblins. It's easy, just build redundant backups in case the goblin gets loose.
Room 1 is the control room. This is a room of arbitrary size where you locate any levers and other things you need to control the pitting operation. Use a one space corridor to get to this room. Line the entrance with cage traps. This is your escape backup.
Room 2 is the pit/staging area. Separated from Room 1 by a levered door or floodgate (The Outer door ). Use a 1 space corridor, again lined with traps. This room has nothing but a 1 tile pit leading to the first level of the dungeon, and a door linking to Room 3.
Room 3 is the dungeon entrance. Again, a 1 space corridor lined with cage traps links this to Room 2. Use a levered door or floodgate, operated from the control room, to control access. This is the Inner door.
To use: Place occupied cage in Control Room. Open Outer Door. Send someone to pit the goblin. This is best done by an accomplished wrestler, if you can manage that. They seem to get away a lot less from them. If the goblin gets loose, he should run straight into a waiting trap. Start over.
To send in your gladiators, open the outer door and station them in Room 2. Close Outer Door and open Inner Door. Change the soldier's station to the farthest spot in the dungeon. Watch the carnage!
I say doors or floodgates, but I only use floodgates. I hear the thieves can pick locks.