After sharpening my blades a few times it gets hard to get a good edge because the bottom of the blade has wear. I a tempted to hit the back of the blade a few licks but I have heard you shouldn't do that. Not sure why. I would have to take off alot of metal if I only hit the top side. I use a file. I decided to take the blades down to the local lawn care shop to get them sharpened and to my surprise he hit the back side a few licks. Just wondering why you are or are not suppose to grind the back side or any other helpful suggestions. Some of the lots I mow are rough so i hit dirt, rocks, etc every now and then so I know I'm hard on blades. Any advice would be great. These are Exmark blades.