Some dogs need to have their glands expressed more frequently than others. Taking him out to go to the bathroom as soon as you notice it may help. If he can express them on his own by going to the bathroom, this will save you some effort and/ or time. This is not necessarily a bad thing, just inconvenient.
could be worms
Worms don't make dogs scoot, as one person answered -- that's an old wives tale. Scooting has to do with the anal sacs, which need to be expressed regularly.