I know what you are saying, had this many many times!! And I’ve had this pblm after I started having sharp edges; sometimes, when you roll your fondant, the edges are pbbly thicker than middle, hence more weight, so when you unroll your fondant over your cake, the weight will pull the fondant down and you get tears. First thing I do now is secure the edges, as soon as I unroll fondant, I run the smoother on top quickly then immediately, I start securing the edges with my hands. If your fondant, to begin with, is too thin, it will tear at the edges and around the cake too (had that too). I have seen many tutorials that roll the fondant much much larger than the cake to flare it out on the bottom so not to have wrinkles; but in my own personal and humble opinion, I don’t do that anymore, I roll almost exactly the size of the cake, just a tad larger, and it works for me; so what I am saying is try different ways and it depends on the shape of your cake, see what works best for you. My cakes are taller now than what I used to do and this is part of the problem, so that’s why I don’t roll much larger; if your cake is shorter, it is much easier. Good Luck!!
Dina @ miettes, http://www.facebook.com/pages/miettes/257790597632317