I have had this done twice now, and the darn cv boot keeps sliding of and making a mess! Anyone have any ideas why this would be ?

 

Spike, normally when a CV boot will not stay on, it is because one of the ends is pulled too far back and it is causing the boot to be stretched too far, pulling it off of one end. I would say that you need to slide the end on the shaft (towards the center of the car) down a little bit towards the tire and then reattach the other end back on to the CV joint. A matter of an inch of movement on the shaft end should be more than enough to keep the boot in place from there on out. May want to ponder taking a little bit of black RTV and using that as a "glue". Then you just have to make sure that the mating surface of the CV joint and the boot are free of any grease and then apply just a little bit of the RTV to be the adhesive. That may provide just enough stick to keep things together. Granted, moving the shaft end is going to be the big thing.