We've always used Sentry, but the store only had the XFT kind in stock. So I bought it. The first time we put it on, our 85lb Lab freaked out. Snapping at his back, scratching constantly...we thought maybe we scratched him with the application tube. So we did it again this month, very careful to not scratch him. Turns out -- this medicine causes some kind of reaction. Anyone had the same problem? I see the complaints for Sentry XFC, but I hadn't found that many for this one (save a few on Amazon that were spot on).