Well I'd just politely ask that they avoid parking where they are and blocking my drive... I don't have these issues up here in the mountains...
At least you're trying to be a good neighbor, there aren't a lot of people out there anymore who go out of their way to act "neighborly."
OP, let me get this straight, you've talked to this guy about his dogs and he blows you off? I love the idea of document everything, take pictures/video, and contact the SD. I know how Jeffco works with dogs that are misbehaving, not sure how it is down there, but if there are too many complaints they could possibly fine or even impound the animals.