Because I didn't want to take any chances with giving the Shelties ivermectin, we used Sentinel during the summer. I can't say how effective if was since heartworm isn't a huge problem here but it did control the fleas (with Sentinel, fleas are unable to reproduce but are not killed). We recently switched to advantage. It seems to be doing a good job cause I haven't spotted a flea in a while. The only thing I don't like about it is that the dogs stink for the entire month.

After puppy shots, I don't like giving shots unless I really need to (laws or requirements for agility classes)