BigT, you are too easily inpressed!
Vinke, are the Koro's a lot cheaper than Hancocks?
Pete, never used a Bailey but believe them to be less effective than a Hancock. Have you ever tried one?
I set any size of dam, made of anything. I think it's important not to tear too large of hole so they won't bring in larger material to repair the breach, such as a big branch or log. I really don't get conerned about the depth of the hole either since I tighten the tension on the pan to prevent the current or debris from firing the trap. Ideally, the beaver comes pushing some mud or carrying a wad of grass but the Hancock can take a pretty good sized sappling, corn stalk etc. and it won't interfere with the trap closing properly. Here are a few beaver from last spring.
Diver, here is a lured set that took the last beaver in a colony...
And the remake. You can see the size and placement of the mud pie on the trap. Any luck today?