Another tip that I learned from someone and found extremely helpful - borderline cheating:
If you want to found a religion but is worried that it may get wiped out (i.e. if your neighbor is Russia/Poland/Spain/Ethiopia/Indonesia/India (Gandhi)/...) then recruit a great prophet and then wait to found your religion until you have a lot of holy sites up and running. Here's the key to why: When you found a religion, all existing followers get wiped in any of your cities that has a holy site, and these cities immediately convert to your religion. This gives you a huge internal pressure of your religion and saves you a ton of faith.
The downside? You will likely found last and have last pick for follower beliefs. BUT, and here's another tip/cheat: There are three follower beliefs in the game that are really powerful: 1) Choral Music, 2) Feed The World, and 3) Work Ethic (ok, 4) Jesuit Education is also very useful, but anyway ...) - so, AI will always pick 1) and 2) first, so unless you are either first or second to found a religion, those beliefs will be gone anyway; and AI never pick 3) (and I'm not sure they pick 4) either - they used to, but I don't think so anymore, at least not on standard size maps). Point is, even if you wait forever to found your religion, you can always get Work Ethic, so you don't have to worry you'll be left with some trash follower belief like Religious Community or Warrior Monks.
For the record, this goes for the other belief classes as well, most notably founder beliefs, where the really hot cuts (Tithe, Cross-Cultural Dialogue, World Church, depending on your needs) will always sit untouched by the AI, while in Worship, you'll always have the juice choice of Stupas (+1 amenity) or Pagodas (+1 diplomatic favor) sitting back at the end.