I just read this whole thread. I wonder how many of the later posters bothered to look at the OP's original problem. He has a Beagle which is overprotective of him and barks at other dogs. Suddenly we are into discussions of e-collars and professional trainers. I would think that a far more sensible approach to this issue is just basic obedience, especially in presence of other dogs. I would suggest just enroll in a local obedience school. (Probably cheaper than a decent e-collar) They are kind of fun, you and your dog will enjoy it and both make new friends. I suspect your dog may have missed some socialization with other dogs as a pup. It is harder to overcome as an adult but not impossible. My wife rescued an 18 month old Rottweiler many years ago that had not been well socialized and had some aggression issues with other dogs. She took it through three levels of obedience training at a local club over a year or so. The change in that dog's attitude and demeanor was unbelievable. She lived a long happy life and had many dog friends after we got her in balance. If my wife could do it with a Rotty I can't imagine a Beagle being a major issue.