I use 10 to 15ft chains attached to a cinder block.I bury the cinder block with chain attached about 3 ft deep.
Because bullsnaps fail,mtn climbing snaps have springs that wear out...I use a 2inch O-ring to go around the collar.Attached to the O-ring is a heavy duty swivel.The small swivels will work but you need to remember the swivels will be in the elements 24/7 and the dog will wear them with movment.The heavy duty swivels will ensure your dog doesn't get loose because the swivel broke.
I attach the swivel to chain and O-ring with extra chain links that have to be pounded shut.
It's not the best picture but you can see here how the set up works.
Using this set-up I have NEVER had a dog get loose.The swivel lets the dog move around without the chain binding up at the collar.Some folks use two swivels but one at the collar is really all you need.
Any more questions just shoot!!