How do you guys know where your drives are in the trim range when you are trimming above what the gauge reads? My gauge reads -1 to +8 but when in shallow water I need to trim the drives higher then the +8 marker. I thought of making my own mechanical trim indicator that showed the full trim range (9 inches at the piston) but the cables i have found appear to only have about 4 inches of travel. So what does everyone else do?

You should not trim the drive that high when running anyway. It is very bad for the U joints. If the water is that shallow, you should not be in it.