Thanks Par, nice to know about the Ivermectin and ACD's. Grant has been on the Interceptor since we have had him and he's done great. Perhaps I will price out the Sentinel and see where it takes me. I have yet to see fleas on Grant, not sure they can get through that hair. I always catch them on Maggie, she has very little hair so they seem to like her. I'll have to see what the prices are at the vet's for the Sentinel. I don't like using the chemicals on the dogs unless it because necessary to treat them for the fleas. If I could get away with the Sentinel and be satisfied with it, I might try it. I'll see what the vet has to say. Thanks again for all of the tips.