I agree with Angel518, at a dog park, rendering your dog defenseless is going to make him more stressed out. If Buster cannot handle being around the dog park, I think it is in your best interest to leave him at home until he can handle it. Being there obviously stresses him out, and muzzling him while he's there would put him over the edge I think. Ritz gets nippy at the dog park too, and gets stressed to the point where he's running around foaming at the mouth and drooling. We won't be taking him until he's ready again, it's not worth it to put him in a stressful situation where he might hurt another dog.
If you want to continue to allow him to explore and socialize, perhaps you can bring him to the park during non-busy hours, or consider finding a small dog park where he doesn't feel as intimidated. My chihuahuas have a totally different personality when interacting with big vs small dogs, and I can't imagine teaching them to socialize with huge dogs right off the bat.
Keeping him on a leash at the dog park may be good to keep him restrained, but bad because he cannot run away if something comes charging at him, and if he bolts, the leash can easily get tangled in a mess of hands/feet/dogs. We recently had a dog come in with multiple bite wounds; the owner had kept it on a leash at the dog park, and it was attacked by another dog, it couldn't run away so it sustained heavy damage, however the owner also was injured, the leash had wrapped around her leg and she was pulled to the floor by her Rottweiler, and dragged around by her ankle in the middle of the pack of fighting dogs. If it were a small dog park, I would maybe consider a leash, but if the park is mixed (you mentioned a malamute), I would definately reconsider.
Good luck! -Nate
P.S. what a sad story about the basset hound =(