#2 is as big as I ever go on land sets. I trap coyotes and fox both, and have caught my share of ranging dogs, including the family pet. Like Dan's situations, all were either where they were not supposed to be, or the owner knew where I had sets and ventured near with their dogs anyway. No issues resulted here, either. Dogs were main reason I downsized to #2s only. I use #2 longsprings, coils, some 1-1/2s too.
Fox look bigger and tougher than they actually are. The have a relatively big foot for their little bodies, but aren't that difficult to hold. I use a lot of 1-1/2's and even little #11s on them with great success. Along my creeks and wooded areas, where coons or fox are both present, the #11 is my first pick for dirt sets. Trap placement is a little more of a necessity with that small jawspread, but I've held a lot of surprises in that little trap over the years. (Beaver, coons, fox, 3 coyotes, and yes my first cat was in one of these #11 guarded dirthole sets for coon/fox). Its way too small a jaw spread to seriously target cats or coyotes with, and any you nab with one will most likely be toe catches...but by sheer design of the longspring mechanically nothing will get the springs backed down or jaws apart once they get in one...it holds whatever it catches, period.
For straight fox sets, I wouldn't hesitate to use #11s up to #2s, and honestly a #2 in my opinion is a bit overkill for fox. I caught a couple in Duke #2 coils this season and the jaws grabbed a little high on them for my liking. 1-1/2's and #2 longsprings actually have relatively the same jawspread and jaw height, and seem to be a decent spread for fox nabbing.
We don't generally get a ton of snow in these parts (though as I am writing this we are getting dumped on) but norm is relatively little snow and bigger jawspreads and 4-coils just aren't needed for fox or land coon work. I think if you start trying to mix coyote-sized traps like #3s, #4s, etc. then you will start hitting issues with your dogs also.
Another nice thing about those little #11s is that some bigger dogs like a big-footed lab, etc. will actually span the jaw spread on that trap, and you get misses when the jaws rise during the trip. I guess in short my preference for fox around here is to scale things down to the #11 or #1-1/2 size, but don't push anything larger than a #2 if dogs are a concern and you have to use whatever traps you have in your arsenal.
Charlie Dobbins often wrote about making "blank" sets for fox in dog areas, too. Make two dirt sets in a location, one has bait or lure and no trap, the other is just a dirthole or small-mound type set with a trap bedded but absolutely no bait or lure. His experience was that a dog would find the bait/lure but not be so interested in the other set with no attractors. He wrote that fox are used to foraging in the wild for food, and just the fresh dirt smells at the non-baited set would be an attraction in itself, as well as the experience of the hole = food in the fox world. I never experimented much with his theories...but an approach like this might also help eliminate some of your dog visits. He had one set where he used a log or fencepost. He made a dirthole set at one end and loaded it with bait/lure, but no trap. Then he made another dirthole set at the opposite end of the log or post, and that one got a trap bedded with it but absolutely no bait or lure. He wrote that surprisingly this set would connect with wild canines fairly consistently and never had a dog issue.
Again, I've never personally tried this much, but thought I would pass along since he was somewhat of a legend among our kind.
Jim-NE
