Yamaha 225dx eating rear brake pads - Help?

[motoman011]

I have an 84 225dx and I'm on my 3rd set of rear pads since I bought it this winter, I'm sure I am installing them right and I do not believe the rear disc is bent in any way, but we will adjust it and by the end of the day I either need to adjust the cable or the bolt and set nut to take up brake pedal slack so they work properly. My son rides it and I've watched closly, he's not using them a ton and he's not resting his foot on the pedal ride the brakes. Any ideas or information on what is wrong? I owned a new one many years ago and I believe the rear pads needed replacing one time, and it seems it doesn't matter what quality pads I use. Any help would be great!

Thanks:(

[HONDA_ATC_FREAK]

I'm not familier with the 225dx but if it is anything like my big red if you ride in sand and your brakes aren't water tight you'll eat the pads right up. But that sounds quick even for sand what brand of pads are you using?