Rarely have I seen so much to do about so little. Why does anyone think the bowls need protecting? The pipes are carved out of briar for a reason. If you smoke so hot you burn a good briar bowl out, you deserve your fate. If there is a large pit hidden just under the surface, it needs to be revealed as early as possible so you can get a refund. If the bowl is sound and you don't smoke like you're trying to heat up a blast furnace, cake will form as a natural consequence. Unfortunately, you have to work to even slow it down.
Pipestud had an excellent post some time back about the practice of coating the bowl with honey, pointed out all that did was cause the sugars to burn resulting in some carbon. Just like the burnt tobacco does. His point was it is a waste of time. I fully concur. I think all the recommendations like honey coating, 1/3, 2/3 then full are for rank beginners who won't dry their tobacco enough to smoke a bowl to the bottom where you form some cake on the heel. Fill the bowl up with your tobacco of choice, dried as it should be, and smoke. The bowl will be fine and the cake will form as you smoke more. Don't over think it, KISS.