Jmo there eather going to get a hold or they ain't its all about what he or she wants to do and are born with if a dog wants to be rough he will show it
I have two pups that are 13 weeks old and are caught when thay see the pig jmo you can't make a dog get rough if he don't want to.
X2
Aint found a way to make em more gritty unless you vest em up and always put em on small hogs to give em false confidence. (That will catch up to em in the end on a sure nuff bad hog).
You can try training with em as puppies to hit the rear instead of ear or head. While teasing your young pups tease em with the pigs rear end instead of head on. I have found it works perty good at gettin em to hit the rear end little more often when you make the pig run from the pups.
Just couple of suggestions works on some and not on others. Good luck