Originally Posted by WarChild

One thing you want to be on a look out for is allergies. Dogs of all ages can develop them. If your dog is scratching or biting at its self a lot, developing problems in its ears or has "hot spots", which are sores on the skin that weep liquid, then you need to re-evaluate its diet. You should note that these things can be symptoms of other things too, like fleas, but if you have a good flea control regimen that shouldn't be an issue.