A fox stuck his nose in a buried MB 550 and snapped it in his face. Now he locates the trap first by sniffing out one edge and carefully exposing it. Then he exposes the entire outer edges of the trap (or traps) and has a hoedown on the surroundings and takes any bait offered.
My latest attempt to fool him was to bed and cover the trap in a horse shoe shaped depression just big enough for the trap. An armored edge is created by naturally situated embedded stones. In the open end of the horse shoe I placed a somewhat fresh cow pie. He tried and could not get at the trap for the rocks, so he carefully burrowed under the cow droppings and flipped them over.

I should write this guy off, but I'm wondering if there is a set that CAN catch him. I tried a campfire ash set--he robbed it. Dirt hole, flat set, blind trail set,multiple traps, etc. He is now getting picky about what flavor bait and lure he will even try to get. I've fantasized about a Caddyshack solution --tracking him to his burrow and dynamite. Just kidding. Maybe.

Yes, I think I should write him off and get some sleep.

Make a dirt hole set with his favorite bait, food in the hole and make an empty trap bed. Do this for a week then slip a trap in on the 8th day.

Blind snare.

Set another trap or two back from the trap he knows is there...and blend it in carefully. I remember doing this to my first fox like this back in 1983 ish. He uncovered my trap 3 nights in a row. Night four he ended up in my garage.

Bury a dead fox in a brushy spot where you can set carefully concealed snares. They will investigate the dead one and dig it up, especially during the mating/rearing season.
Your fox is keying off on everything you touch and bury and probably your attractants. They can smell your trap through the dirt. All canines can, but they have no reason for concern until they get pinched.
I do nuisance work which requires me to catch all of the fox/coyotes, not just the uneducated ones.

An extra trap has always worked for me. Just make your normal set and carefully blend in an extra trap where he stands when digging out the trap.

one word.

SNARE.

he sounds smart so set it up with rubber gloves and use a small diameter. i use bobcat snares for my fox.

blind trail set

Lots of good advice but I like strike2x or the snare (if legal) advice. I'm no expert but prob. the best advice is to write him off A dumb fox pays just as much as a smart one & is a lot easier to catch haha!

Keep trying with a foot hold it would be a shame to waste a learning experience and good animal with a snare, you won't loose that much money! I'd blind set with all the care in the world,or 2 traps had a grey give me all kinda of fits in Pennsylvania one year got him finally in a carefully blended blind set in an other wise featureless field just a coon trail going thought it, he would find them if I set in to much cover so I had to get in short grass it was a good learning experience wish I hadent sold him eny who my 2 cents
Colt

I agree snares would probably be my best bet, but right now I don't have any fox size . A fake trap bed over a week is a good bet if I want to keep after him another week--which normally I would. But I'm focused on yotes this year and trying to hit a set goal. Don't want to spend the time.
One set that has worked before on lesser educated fox is a fatty pork bone half charred and driven in solid or staked and a couple traps buried near it. Maybe the smell overwhelms their ability to detect the traps.
Taking the time to track it in the snow to pinch points for blind trail sets or a snare ambush might work. Right now all snow is gone.
The present set location is a south facing rocky hillside pasture with no cover and close cropped grass--like 1/2 inch high right now.
I'm thinking I'll see him again on the line next year.

Thanks for the good suggestions.

Did you ever hear of the windup clock set. A small clock buried in a container with the trap directly on top of it, a few feet away from your other set. You have to do this every day because the windup clock only lasts for one night. They usually dig with both feet. Ive only used it twice since trapping. Worked both times.make it like a flat set blended.

Fox like to use small hills to their advantage when they can. Make your set like you usually would, but make it about 8'-10' from a small rise or mound. Now carefully make a blind set on top of that mound. Fox will be focused on your set and use the mound to look things over. With luck your fox will be waiting for you.