One of the fundamental causes of unwanted behavior in dogs is frustration due to a lack of exercise. When a dog is left in the back yard or house all day, every day he starts to go a little nutty. I can see a difference in my dogs after one day without exercise, so if you have gone weeks or months your dog is freaking out.
If you really want a well behaved, balanced dog you have to exercise their minds and bodies every day. How long depends on your dog’s health and energy level. A healthy, high energy dog can easily walk up to 10 miles at a time, so you must start with 1-2 hours of exercise every day. Lower energy dogs can get away with much less. Energy level and health, not age should be your guide. I once worked with a 9 year old shepherd mix who had attacked her owner while she slept. She could do a 2 hour hike in the morning, followed by 2-3 hours on a treadmill, and was still first to the ball at play time.
This dog was such a problem because German Shepherds are bred to work 8-10 hours a day. If that need is not fulfilled, they will fulfill it themselves. Dogs that have become aggressive out of frustration are some of the most dangerous and often become red zone cases. To ensure your dog does not reach this level of frustration you must walk them every day. Dog parks and daycares are good ideas but nothing burns energy like a long proper walk.
The primary benefit to proper exercise stems from the growth of the leader/follower relationship. You should always be in front on the walks because whoever’s in front is in charge. The reason most dogs pull is that we allow them to. If you don’t communicate rules and boundaries on the walks you are telling your dog there are no rules.