I believe it's genetic.
I'm not saying you can't make any one of your dogs roll out, but it's an uphill battle, I know I been there. It always helps to have an older dog that will roll out, but just don't let the dogs stay chewing on a hog. A leash works wonders when the dogs won't leave your feet, make it uncomfortable for them to be there if you are by yourself. If you are hunting with someone else, catch the dogs and walk them away coaxing them to go hunt, if they go back to the hog whip them off a caught hog, they'll learn the difference and it won't hurt them.
agreed