dog rubbing rump

Question
my 3 year old mixed teareor is rubbing his rump on the ground and seems irritable lately, what could be causing him to do this?

Answer
The problem is often the anal glands.  Sometimes worms.  If you see any eggs in his stools or clinging to his anus, you could try an over the counter worm medicine.  If you have him on many of the heart worm medicines, such as Heartgard+ or Revolution, they clear out other worms before they can establish themselves.  

Best idea is to take him to the vet and identify the problem and take effective action.  Often it is a matter of emptying the glands.  If it reoccurs, some groomers will do it too.