Kenai used to get sebaceous cysts all the time. They would feel hard but be mobile in the skin. Basically a blocked up oil gland. If you are concerned about it however, it never hurts to have it looked at and evaluated. Dogs can get a lot of different bumps under their skin. Some kinds of masses they can get require fairly deep margins to avoid reoccurance or spreading. Some things turn out to be nothing. But I personally always feel better safe than sorry. >> I may be a touch of a worry wort kind of momma lol.