Hi Scott, 

>how do you avoid tearing out when you put on a bevel across the grain?  

OK, maybe tearout is not the correct word. Blow out, splinters, divots ?
In difficult hardwood this occurs sometimes along the edges when using
a scrub and planing along a diagonal. The bevel is planed along the edges
"with" the grain first, then planed on the cross grain edges. No blow outs
at the ends. I use the bevels mainly for a visual reference. I can scub/plane
a lot faster without having to bend and squint at the gauge lines. Insurance
against blow out is secondary. The final plane strokes, along the grain, with
a #6 or #7 bring it to the final thickness.

Best,

Louis Michaud
Rimouski, Quebec