is the pup running behind your older dog yelping or is it carrying on toy fighting growling etc ?
my whippet cur basicly terrorises my collie cur when they,re having a carry on, its all part of the pup growing up, its learning to run and strike etc but it thinks its play which is perfectly normal
The age your pup is at the moment I would wait until September and then start to take the pup ferreting, net all the holes if you can and let the pup grab the bunnys in the nets, this way the pup thinks he is catching the bunnies, builds confidence no end, confidence is what the pup needs at t