A dog attacked mine at the park, my dog wounded significantly, other dog fine but owner has a bite, claims it was my dog- help?!

I have an old boxer and for years he's gone to local dog parks. He can't run-he wanders and is friendly. Most of the owners know he's a sweet lush.
Last week a golden got loose and mauled my dog (spring). Spring didn't understand, didn't even defend himself. I had to pry the Golden off my dog, who had gone for his neck His owner had him, I went to pick up my dogs collar the golden had broken-The owner lost control(again) and he attacked again Spring was bleeding badly-I finally got the dog off Spring and ran to the car to take him to the vet. 7 major punctures-stitches,drains,surgery
The owner claims the 2 bites on her arm are from my dog (I don't believe it) refused our vet bills & called the police. Her dog has attacked before but no police reports. How can I defend my dog and myself?