I personally try to choose trails based on having a dog along. I don't know your area, so I can't speak to that, but I choose less spectacular hikes in favor of creek-side hikes to nothing much. There is one I go back to regularly that is down inside a gorge and the rock cliffs really keep it cooler even in the heat. 

If that's not an option consider car camping and a small kiddie pool for the dogs to cool off.