As a confirmed "Bodger" of all things automotive, I have had to resort to using exhaust repair materials many times. I have tried all sorts of "Own brand" repair bandages, but always go back to good old Holts Gungum bandage.
The beauty of this bandage, is that you simply throw it in a bucket of water, allow to soak for a minute, then wrap it around a leaky exhaust, and bind with the wire enclosed. The instructions are on the box, and the bandage does not contain Asbestos.
The bandage itself, does have a shelf, but this is several Years. If the bandage is old stock, or if it is a very cold day, it should be saoked for a little longer. It is difficult to explain, but you will just know when the bandage is supple enough to use. This is to repair a small hole or a few pinpricks, anything more than that and you will need another Holts product.
If used correctly, to cover small holes, this repair will outlast the rest of the exhaust system, but make sure you are not trying to throw money at a corroded pipe, which is in need of complete replacement.
After repairing with this bandage, it is recommended you run the engine to "Bake" the bandage until it hardens. Once this is done, it is solid, strong, and should not flake off with the heat. You can also buy tins of the Gungum paste, plus other repair systems from this Company.
The exhaust of a car gets a lot of acid fumes through it, and lots of water and road grit from underneath, so it will rust if not protected. They normally come coated against rust, but you can keep them protected for a bit longer by using paint. You need paint that will withstand the heat of course, recommend Hammerite.
I also recommend Holts Gungum Exhaust Bandage.