Help with axle!!

[00Trx400ex]

Hey guys, Been ridin bikes most of my life and recently sold my bikes and bought a 400. Its an 00 and is bone stock except for wheels/tires and the durablue +2+4 axle. I had no problems with it until lately. I noticed my axle locknut was backed out allowing the carrier to move back and forth on the axle. I was looking at it and noticed that the locknut is not threaded its splined. It just slides against the brake hub and there is no way to keep it there. The locknut just backs out and sets against the stop ring. This might be an easy thing that I just dont know about but would like some help. I am putting new axle bearings in tommorow and would like to get it solved for when I put the axle back in and get it all together. Thanks for the help guys.

[BlackTrx440ex]

theres a clip on the right side of the nut when your looking at it from the rear and that holds on it but some how the 2 nuts together stay on there and the inside one when your done wrap it in tape and it wont come loose anymore