Run rubber boots with leather covers. The rubber can crack and the leather will contain the grease.
Double stitch the side to make a "cone" then fold in the ends before double stitching the ends. Then simply use metal zip ties to hold the metal.
Every couple of years grab your junk shop vac and suck the old condensated grease(it happens anywhere there is air) out replacing it with new.
If the rubber boot cracks let it crack. The outer boot will keep the grease in.
Eventually you will need to replace the boots if they continue to crack due to being pulled or such because they are to short. But if you install the proper sized boots no matter the quality and then install leather covers that will greatly contain the grease within the boot area.
I will note that the homemade leather covers I talk about making above are not intended to be submerged. But for general street driving they keep your ride looking good. Being able to be made in a variety of colors (if the boots are highly visible) is also a nice perk.