What is the best health insurance for dogs?

I have two rotties brother and sister 51/2 years old and a rottie/mastiff mix appx. 4 years old and vet. visits are starting to cost alot, ex. one just had a biopsy 400.00 plus another has an infected gland (gross) 200.00 plus, will insurance cover these conditions? Side note if anyone a dog whisper type trainer my two males fight and we have to keep them seperate. Thanks for reading.