Thanks everyone :)

I've tried to get sharp stakes + pit to work as a trap. Does not work with trolls, they basically ignore the stakes or demolish them in one hit. Either case the knockback is negligible. For other mobs I have gotten it to work.. unreliably but occasionally. Manged to capture three skeletons in a raid, about the same with grey dwarfs. Still working on the concept.

Best success I've had in my experiments has been following up on the obstacle suggestion from @Cap'n Bells replacing natural obstacles with artificial ones made of 26 degree X pieces at different angles spaced far enough apart that you can fun through but trolls and other large creatures can't. They don't seem to be very apt to destroy the X pieces, rather they walk around.

Going to try a variation of the sharp stakes and pit for smaller mobs with trying to protect the sharp stakes from all but one angle. I'd really like to get sharp stakes to be useful but its not easy.

Thanks again, and please keep the comments coming. It is great to see how other players solve common problems.