Theres a few solutions, clean the piece more often, get a new downstem with larger holes, use a bowl with a built-in screen or put screens in your bowl, or use an ashcatcher attached to the piece to filter out the ash and plant matter that may come through the bowl piece.
We have noticed that when doing dabs the small holes can clog even faster than by combusting a bowl. This is done to the fact that the fats and lipids cool in the water and when the vapor goes through the small holes that is when the air has the most contact with the surface of the glass, hence this becomes the place to clog first.