My dog bites other dogs at the park. Is it aggression or excitement?

This is a serious and potentially dangerous situation and I recommend you enroll in some behavioral/socialization classes in order to create some positive behavior patterns. I do not recommend any rough play at this stage and only use exercise and toys which do not create such heightened excitement - do not encourage any tug games or chasing of ropes/toys in hand or of your own hands/feet shoes under any circumstances as this blurs the lines of acceptable behavior and biting/chasing behavior. Ensure he is receiving adequate physical and mental stimulation daily in order to fully engage body and mind

Walking them in neutral areas away from his normal routine and territory can help to get dogs used to each other in a less confrontational manner and can help in such cases, I would recommend muzzling both before allowing free play to prevent injury initially. Do not leave them unsupervised or loose until they are more accepting of each other

Aggression towards other dogs is usually a result of not being comfortable around them - it can happen due to a lack of socialization as a puppy, a bad experience with another dog at a young age, or even a genetic predisposition to this problem. It usually starts to appear around social maturity, so if Max is about a year old, this would be a very common age to begin seeing this problem. Aggression issues are complex and difficult to address succinctly in this format, so I would really recommend making an appointment with a veterinary behaviorist if at all possible - he/she can evaluate Max in person and help you put together a treatment plan to work on this problem. In general, I can tell you that treatment will involve teaching him to associate good things with seeing other dogs and behaving calmly around them - we normally use food rewards and other types of positive reinforcement to achieve this. Punishment for this behavior is not recommended, since it tends to make the dog more fearful and worsen the problem over time.

If Hondo gets into a fight every time he's at the dog park it would be best to discontinue going. For some dogs, the dog park is a high-stress place and it may not be for them. Other ways to exercise can include solo walks, fetch in secluded areas, and even focused activities that don't involve other dogs. If he's having trouble with the new puppy, or is severely dog aggressive/reactive it would be best to talk with a trainer or behaviorist in your area that can work with you on a plan to help get him more desensitized to other dogs, and potentially doing OK with some. In the mean time, if play gets too rough or one or both dogs seems agitated, taking a break and separating both dogs until they've calmed down is best. Make sure not to leave them unsupervised together as even the sweetest dog can accidentally injure another! Since aggression toward other dogs is a complex issue, it is best to work with a trainer who can supervise your techniques and plan in person.

Some of this may be curiosity and not knowing manners on how to act around new dogs. Some dogs have a different personality and manners on a leash vs. off a leash. She is young enough that seeking a trainer to help socialize her both on and off leash, in new settings, and around new and familiar animals will help her behavior. The more interactions at a young age, the better as long as they are controlled and the proper behavior rewarded

Because Milo is still so young there is definitely time to correct her aggressive behavior. You should start with basic training commands (sit/stay/come) to help establish the fact that you are the one in charge. It is also important to make sure she is getting plenty of exercise. You should take her on fast-paced walks for 20-30 minutes at least twice a day. I would also recommend that you seek the help of a veterinary behaviorist to help you identify and treat Milo's underlying problem. Good luck.

I strongly recommend enrolling in some solcialisation classes run by a certified trainer or behaviorist in order to improve his interactions with other dogs and his focus on your commands. This will take a lot of time and patience on your behalf given his is fully grown now, I would also consider neutering him as long as there is no fear/anxiety in his behaviors - ask the trainer to fully assess before you schedule this and consider a temporary castration implant initially which will reverse over 6months or so if necessary