Canine Aggression

[tcmutts]

My fox terrier has always been a bit growly, mostly when eating (I assume because he is "protecting" his food and sometimes when sleeping either in his bed or at the foot of mine. At those times I just stay out of his way. But recently he has been growling more, and baring his teeth occasionally, especially when he is asked to move from a comfortable position. He got hit in the head some time ago accidentally by a kid swinging a bat, and seemed to suffer no ill effects. But I'm wondering if that might have something to do with this. I'm going to take him to the vet this week but I'm wondering if anyone here has any thoughts or experience.