It has been so dry this year, we haven't seen too many frogs/toads and wouldn't you know we have an over abundance of crickets. Of course, my dogs eat the bugs but leave the frogs alone.
I don't know how you would stop them. I've never really seen dogs bother them after a few foamy mouths they kind of learn that they taste bad. I don't know if you make a big deal about them in front of the dogs, they may be thinking they are protecting you from them if you get excited when you see them. I don't know, it's really just a guess. I wouldn't like mine putting them in their mouths either. Yuck! Good luck.