DEX210 wheel axle boots- problem

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I bought the Durango "driveshaft boot wheel axle" rubber boots to prevent dirt/sand from getting into the CVD assembly, and creating a grinding paste with the grease. I greased the balls and cups carefully and put the boots on either side. However after a quick run the larger end of the boots slip off the ridge they are supposed to sit in, and leave a gap. Has anyone had this problem, or a similar problem on a different car? Am i doing something wrong? Is there a fix to the problem?

Any help would be appreciated,
Ed.