Boddicker wrote about guys who could place a trap on a rocky surface, camouflage the pan, and catch any coyote, bobcat, or such that visited the trap site. You don't seem to have a problem having some quarry to visit and get caught but aren't having luck holding them. Again it sounds like coons too me. The reason I mentioned Boddicker is he hits on individuals that knew their target's foot movements and how to get them where they wanted them. That will take time and experience for everyone to master. How the animal reacts to an attractant is a learning process so use snow, mud, wet sand, game cams, etc.,,,, anything that will help you see how they place their feet at a trap set. You won't learn that on Youtube. If you believe its still canines pulling out and you have examined the "gear" for reliability, try focusing on their foot placement. I ran a scent post survey for the Nebraska G&P in 4-5' circle patterns in the Spring for several years in the 80's and learned much on an animal's foot traffic at an attractant. August Heller from Dunbar Nebraska caught coyotes on frozen farm ponds (the water not the dam ) in the 60's and 70's and I stumbled on his method then. Took me a few years to absorb what/why he did what he did but he got the "foot" where he wanted on that smooth surface. He knew coyotes! Keep observing and you will do fine. ............................................................ the mike