My now 67 pound rescue would run over small dogs at first and when he was 75 pounds.  This is probably because his first two owners were not his leader, didn't teach manners and encouraged excitement which is often confused with a happy dog.  Since the problem involved dominance I would roll him to the ground and pull his tail out of the way for the victim to smell his rump.  I've been investigated by the OSPCA and local Animal Control for abuse because I would do this.  When the officers learned I was the third owner and the reason for my intervention they were satisfied and also impressed with my dog's good behaviour.
 
I walk my dog plenty and in a structured manner and feed him before we enter the off-leash.  He doesn't go through the gate until he is laying down calmly.  The dog park is a social area and that means it is just a form of affection.  Most people take their dogs in there for exercise and that makes for many problems.  My main focus there is to protect my dog.