Brave submitted this

Tired of your flies wandering off and getting themselves killed? Stick them in prison, or, stick them on a guard post until you want to scout, then possess them and DIY - much less fly carnage that way. Guard posts are excellent ways of keeping problem monsters in check - like those darned spiders who insist on hogging the training room or freezing prisoners when you're trying to starve them. Also, if you don't want to destroy your training room but want to suspend training until you have more cash, just be sure to build them in an area suitable to be blocked off with a locked door without cutting monsters off from food and lairs. Lock the door, chuck 'em all out and bob's your uncle.

Making it through the secret 8th level!