Martial Arts classes- These are by far the best stress relieving activties a dad can involve himself in, because it's more than just kicks and punches. These are disciplined, focused activities that can channel you energy into a more controlled flow of energy and power. I have enjoyed practicing martial art techniques for years. As far as a recommendation, my former teacher is 80 something and doesn't teach anymore. The best bet is to check out some styles of Martial Arts you may be interested in such as Karate, Kung-Fu or others, just check the phone book. Most martial arts schools will let you sit in on a class to see if their style would be right for you.
Yoga- Some people swear by these fitness classes that they can help relieve a lot of stress. I have tried one or two classes myself so just check the phonebook and see if you can try a class out.
Join a health club The are many health clubs with different prices ranges to check out, word of caution don't sign any long term contract unless your sure you like the health club. Most health clubs with let you try them out for a week or two.
Just Exercise- Exercise is the single most important thing you can do for yourself for your health and well being. It really doesn't matter if you jog, walk, run or just do some push ups in your home, just get yourself moving to reduce stress.
Meditation- For some individuals this stress relieving technique my be too controversial for them to consider this as a way to relieve stress. However but it does have some merits in the medical community as an accepted way to calm down. Check out this stress reliever technique at the library or online use at your own discretion.
Just Join a local amature sports team- Instead of being a couch potato, how about joining a local team and put your abilities to the test. Check online and see if you can try out for a local basketball, football or hockey team. I will be adding links to some local teams websites very soon.