You can never guarantee a front or back foot catch on a beaver.Setting shallow will get back feet from time to time.It often happens when a beaver does not get caught on the approach but gets caught leaving a set.
I never seen a drowned beaver wring off a front foot.I use positive drowning systems only for beaver in footholds.
Of course front foot set will sometimes get a back. I suppose in an absolute sense it is also true that a deep water back foot set will get a front, but it is so rare for me that I don’t remember the last time, if it has happened. So I can [almost guarantee a back foot target setup wont get a front. Crazy stuff happens on rare occasions, so I wont say never. I will say never to catching a coyote in a body grip at the bottom of a 6 foot deep beaver run. Thats a hard never. I think.
Never caught a coyote in a bodygrip, I did drown one in a spillway set when in high school though. Yeah you will occasionally get a hind foot when setting shallow for a front foot, if I know the water is shallow for a hind foot drowning set I will be more careful on my trap placement to try and insure a front foot, but it is never 100%. Pretty good on spillway sets though. I catch more incidental hind feet on castor mound sets, but then again if I am making a castor mound myself instead of setting blind where beaver are using like a dam spillway, I will be making sure I set it where the deepest water is available, so I am not as particular about targeting specifically front feet.
The only time I have ever found a front foot in a trap is one time when the pond froze over leaving only enough open water for the beaver to stick his foot in the trap and not enough for him to go under the ice and down the drowner. I still suspect he would have managed to break the ice and go down it before wringing off if a bobcat hadn't came along and removed him from my trap first. I've caught tripod beaver, but I can never recall tripoding one myself. I don't use weights often, mostly use stakes on the deep end of the drowner, but when I do use a weight I figure 50# minimum. I did have a big beaver pull up 50# of window weights and be sitting on the bank one time, learned not to use smooth weights that will roll on a hard bottom.