Definitely off grass and use the laser or gps you use when playing your rounds. I use our clubs practice area, green staff and committee are not keen on members practicing on the course. Mark 10 of your practice balls with a number 1, 10 with number 2 and 10 with number 3. I normally start with pitching wedge and hit the 10 number 1's. 9 iron 10 number 2's and 8 iron 10 number 3's. I use a Garmin watch gps with a distance function that's set to zero at hitting area. When I walk down to the area where the balls are, I eliminate the poor strikes and find the middle of the number 1 balls and that