This scene was a great hit. I used a 10ft x 10ft fenced dog kennel. On the side that the guests would approach first I put up black plastic to cover that whole side that way the guests didn't see the scene and it was a suprise scare.
Not only did I cover the side they would see first but, I also covered all the sides but the front. I sprayed and splattered red spray paint all over the black plastic. Threw in bones on the cage floor. Had a "monster sounds" cd playing. And had a strobe light set up accross from the cage (which you could have hooked up to a sensor). When the guests came around the corner to the front of the cage the monster would come to life, he could also open the cage door (that looked like it was chained shut) and chase guests too.
Here are some pictures of my caged monster, which is also my dad!