Regular sand-filled systems don't work and are too hard!  ProGreen's Tee-Lines and Hitting Mats use only 1/4" of sand, just enough to support 1.25" high yarn pile.  You can hit down and through the ball; the club face won't bounce off the surface!  Also, a real tee can be inserted anywhere on the surface which helps to evenly distribute wear.  RT990 is available as both a tee-line surface and as a hitting mat.