I've used it on my 3 at times. It has a bit better effect on ticks than some of the other spot treatments. Usually works within 24 hours if ticks are already embedded and it's fairly waterproof after 24 hours.
It's important to be sure that your dog doesn't have any issues before you apply it. Dogs with compromised immune systems, severe allergies to just about everything, or similar conditions probably should not have any type of spot treatment applied, but if your guy or gal is healthy, then it should work for you.
If your main problem is fleas, there may be a better product and a better way to attack the problem. I'd check with your vet for that.