To start off, I'll give some background information. I'm 16 and my family has two rescue mutts that we've had since they were about 6 months each. We got the first one six months before the second and they get along without a fault, love each other. Both the older and younger one had been to the dog park multiple times with no issue before. When separated, the older male gets extremely anxious and begins pacing and watching the windows till the younger female gets back. The younger female does not do this. We also have the issue of the older male being extremely protective to the point where he will take me down trying to go after another dog, but only if the other dog approaches me or the female too fast. A couple weeks ago I took them both to the dog park, thinking it would be fine because they've both been before just not with each other. When we got to the park another dog ran at me and my younger dog to play and greet us, and was immediately attacked by my older male before I had to physically pull him off. What can I do to curb this aggression? Would it be cruel to bring him to the park with a gentle nylon muzzle and then take it off eventually when I know he wont attack again? Both are large dog mutt breeds, with Great Pyrenees, Sheep Dog, and Ardiel Terrier