sweet beagle

You should really get a behaviourist to analyze his behaviour and give ideas how to fix it. Aggression of any kind is not something that can be helped online, it has to be seen in person by a professional. But until you get that done, never let the dog outside unless he is on a leash or a longline with you supervising him. A muzzle might also be a good idea to keep him from hurting other dogs. That way you can still have some control over him. The more he attacks other dogs, the more of a habit it will become and the harder it will be to break. Chances are your dog will never be fully comfortable with other dogs around, but most dogs can be trained to at least tolerate other dogs without lunging at them and biting.