Some that I have done:

-trapped some mice in cage type traps... then immerse the cage in water to kill them. Works well with rats too.

-trapped mice in fly-paper. After a while they sometimes get some glue on their nose and suffocate themselves.

-trapped mice in fly-paper. Then use some lighter fluid (or gasoline or paint thinner) and ignite a fire

-shot a rat with an air-rifle at night. The rat came out in a regular schedule, I waited for it and shot it with a double action pellet (the type that explodes).

-a mouse got trapped in a plastic trashcan. Sprayed some "contact-cleaner" (only thing handy at the time). Vapors of contact-cleaner seems to be heavier than air because mouse suffocated when I came back to check.

-trapped a big rat with a couple of brooms in our driveway. Called our dogs. I let the rat go. Dogs go after it. Dogs slammed it a few times on the ground, killing it.

-medyo hightech: made a IR sensor connected with two metal meshes with a high voltage source. Installed the contraption at the entrace of a rat hole in our garden overnight. When the IR sensor is interupted, 500volts runs thru the meshes for 60 seconds until power is automatically cut-off. Made this during summer my college using electronic kits. What some people do when they are bored... they invent a better rat trap. :mrgreen: