1. make a moat of lava with a bridge over it and hook some pistons and drop.
2. put your base underwater and put only Redstone torches so it does not put off to mush life .
3. put a anvil above a door and drop it on there heads .
4. make a house in lava and put signs then take a leap of faith .
5. put some gravel so when they walk over it they fall .