I play Paladin/Hunter/Death Knight, and Wizard Cleaves are a *scary* matchup for us. Oftentimes they focus me because I have to charge to them to do any damage, so it's my responsibility to be able to LoS when I need to. Having said this, the way I do this as a Death Knight is keep close watch on what defensive cooldowns I have available (more specifically AMS and AMZ). I'll rotate them, and if we haven't killed anything yet (which is likely, we usually at least get some trinkets out of them) them I'll tell my team that I need to back out and LoS until my defensive cooldowns are ready again. Patience when playing against a Wizard Cleave is very important, because if you constantly try to apply pressure they're going to beat you at it and someone is going to get globaled.
Keep in mind that Wizard Cleaves start drooling at the mouth when they see someone out in the middle of a map, so positioning your team in a way that you can attack theirs while providing an escape route is pretty important. On Blade's Edge I usually charge to their side of the bridge to force them into that area and when I need to bail out I'll tell my healer so I can get the necessary dispels/freedoms to get away from their team. Dalaran Arena provides some awesome boxes that if you can pin their team against you'll be able to quickly move around them if need be. Nagrand is similar to Dalaran, don't get caught out in the open and hug the pillars to get away from them. RoV is Wizard Cleave heaven, pray you can get them locked down before they get started =/
I hope this gives you a little bit of an idea about LoS and positioning, I don't know exactly what comp you are running and if you have any specific questions about LoS feel free to ask here :)