I tried Sentry natural Defense (flea and tick for dogs over 40 lbs.) It's natural, I actually like the smell and it may do a good job. I never found out. The first try, my shepherd/lab mix's fur started coming out in clumps on her back (2 days later). I reported it and they told me to bathe her w/ dish soap, use Vit E and ice packs for inflammation. I tried it because I did extensive research through vets, naturopathic vets, and valid online sites on other pet flea and tick products due to carcinogens and side effects that conventional meds cause. I can't use Advantix because I have cats and it could kill them if they groom the dog within 12 hours or so after I apply it. Not taking chances, thank you. It also can cause skin reactions, contains a carcinogen and could put my dog into convulsions. Bio Spot, Vectra 3D, ParaStar Plus (which contains WAY too much medicine) and many others are just as bad or worse. Frontline Plus is the least of all the evils, so I guess I'll go back to that since it didn't cause reactions the first time I tried it on her and I know it does work on fleas and ticks from experience with my last dog. It can cause thyroid cancer over time though. I won't try knock-offs like it (Fiproguard, Pet Armor Plus) since they have many undisclosed ingredients which could be toxic. As soon as it's not flea and tick season, I'll stop again. The less meds and vaccines for our dogs the better! It's killing them. Vets have got to know that if most people do. It's common sense. They are trained by drug co's that market to their vet schools to say/think that the benefits outweigh the side effects. BS. How come dogs in particular used to live longer then? Drug co's say that with dog's life expectancies growing LONGER (?!) that cancers and disease also rise with it. Look at the facts. They've lost many years of life over 2 decades and the only changes made since our parents had animals is that we vaccinate them more and have all these chemicals we are supposed to put on them in order to be considered "good owners" now. Scary. I remember when we used to spend about $60/year in vet bills per pet. Don't you? I lost my dog last July to a rare cancer. He had a tumor in his heart that bled out and put him in shock with no symptoms or warnings even hours before. Perfectly healthy 9 year old lab. Explain THAT to your 5 year old why her best friend died. Older, yes. but we looked at his food and had our well water tested. The only thing fingers could point to was Heartguard Plus which is known to cause cancer over time. That's why I'm using Interceptor now, again the least of the evils. If I didn't live in CT in the woods with high populations of fleas ticks and mosquitos, I wouldn't use any of this. I implore all technicians, scientists, engineers, "green consultants" and anyone else in this field to PLEASE COME UP WITH SOMETHING GOOD-and that's affordable. But as we all know, that's another story...hope this helps all who read it. Blessings.