The CV (constant velocity) joint boot on the drive axles? I wouldn't attempt to patch those... just replace them. CV boots are cheap. Be sure to grease the CV joints before you put the new boot on.
If the CV boot is damaged and dirt/water gets into the CV joint (dirt will get into the CV joint grease), the joint will eventuall wear/fail (and you'll hear it wearing). CV joints are much more expensive than the boot. This is one of those repairs which you should catch/perform early.
First of all I have no idea what car you are working on. A boot that is broken or missing will allow dirt and water in which will slowly wear out the joint. A worn out joint can usually be detected by a popping noise in the axle when you turn the wheels all the way and drive in a circle. Repeat in either direction to check and listen for the noise. If you have a popping sound the joint is worn out. In some cases it's cheaper and easier to buy and relace the whole axle with a remanufactured axle from a chain auto parts store. Many times the price and aggravation of installing a boot or a joint just isn't worth it. Plus the reman axle will usually come with a lifetime warranty.
If the joint does make a popping sound it is worn out already so driving a little furthur will be OK as the damage has been done. On the other hand the joint itself can fail and when it does the car will not move as the axle shaft will spin in the joint and not power the wheels.
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