There are two ways to handle this. The right way is engage the notches on the side threaded of the washer with a spanner wrench. While a common bike spanner wrench is to big to hold the washer in place, there are other options that were discussed in a previous (which I couldn't find right away)post (pin and hammer, pliers); I use an AR-15 spanner wrench. http://www.amazon.com/BARSKA-AR-15-S...tool+or+wrench



The other way is to insert a thin keyed washer between the locknut and threaded washer.