Lots of gray fox here in SE GA. Seems to be a pair behind every bush.
No set will out-produce the standard dirthole, although I do not use near the larger "gawdy" blocking/fencing as some do. I have always kept the foot guidance somewhat subtle. Most grays seem to work the set hard. When there is a miss it is not a track or two on the pattern as with coyotes, the pattern is usually stomped all over and the fox was very lucky to miss the pan. The curiosity of the good smells coming from a hole in the ground is the key to keeping them working the set a little longer. I have experienced a lot of rubbing on flat sets by grays.
Castor-based lures, sweet(mild) skunk odors, fishy smells, all work great. I never spend money on grey fox urine or grey fox gland lure. I use only red fox & a little cat pee.
Some seasons I will "hit" three or four gray fox "pockets." These small areas (usually less than 200 acres) have produced 10 to 25 grays in a few nights with about 6 or 8 traps/sets. Most grays I've caught in the same trap/set is seven in eight nights. Only found one of these fox pockets this past season.....15 grays/100 acre property/10 nights. Most locations here will produce a pair or two every season. With the grays smaller home range, most of my larger tracts produce dozens of grays annually. We have few reds, usually catch one red to ten grays.
The most important factor in gray fox trapping is location, especially if you do not have a large population of 'em. Here everywhere is "brushy/woody", hence the good grey population.
Here is slightly over 100 finished grays (& other fur) from a couple years ago. Had good weather for several weeks that season so I could access some good properties.
A frosty double