By way of background, my high energy rescue Terrier mix (thought to be Jack Russell x Whippet) loves to run and obsesses over squirrels. Rabbits, chipmunks, birds and the occasional fox are great fun, too, but nothing excites him like squirrels. I have a dog tolerant park across the street, which has an abundance of oak trees as well as concomitant squirrels. I let him burn energy by running after the squirrels on a 26' Flexi Freedom leash, and he often takes a 50' run at them. In the past, this has resulted in a number of broken leather collars, which was not only expensive, but resulted in a dog running loose with no tags. To prevent that, I've resorted to using two collars. His full time Perri leather dress collar holds his tags. The second goes on with his leash. At first, I tried a standard chain collar for its strength, but wasn't too happy with that as the dog dislikes having a collar placed over his head and, worse, the chain is hard on his neck when he hits the end of the leash running full speed (something he has learned to avoid most of the time, but not always). Standard martingale collars alleviated the later somewhat, but not his aversion to having a collar placed over his head. Regular snap on collars were okay, but unless I make them tighter than I prefer, they tend to slide over his small Whippet-like head when he decides to back up. I finally found these, which are exactly what I wanted. They are pricey, but seem to be very well made and likely to last a long time. They snap on quickly and smoothly (not all snap-ons do), and fit him comfortably. As someone mentioned, they do seem to run a bit large. At its minimum circumference, the small size does not squeeze my 21 lb. dog's 12-1/2 inch neck (indeed, the collar measures nearly 13 inches at its smallest setting by my calculation), but it also does not slide over his head, so it is fine for my purposes. I have no doubt they'd serve very well as an everyday collar for those with more conventional needs as well, but you might need a size smaller than you think.