Yep..I'm pretty sure everyone's going to give you the same answer.

I'd stick to spaying rather than the twice a year injection. I don't think many people have heard of the injection, therefore it probably is fairly new on the market. Spaying is a very common thing that almost always ends up with good results.

If you check your local shelter, they may have a spay/neuter program that will spay your dog for you for a cheaper price than some vets. I think the spca here said it was 50 dollars compared to our vet for 100.