I do this with my Leopard Geckos, well, somewhat. I put one male in an aquarium and one on the outside and let them try to go at it. They don't get injured and eventually one of them gives up...leaving one of the males feeling dominant.
-----
Reptiles:
2.2 Leopard Geckos
0.1 Ball Python
0.1 Bearded Dragon
0.1 Box Turtle
0.1 Corn Snake

Bird:
0.1 Jenday Conure

Pups:
2.0 K-9

and lots of tropical fish!

-Patrick