To get crisp, clean white socks, first clip the white marking with a #10 blade. You have to be pretty skilled with the clippers to blend/feather the clipped white sections into the dark sections. After you've clipped, shampoo the markings and powder them with either corn starch or baby powder - this makes the socks pop out, and protects against some staining.
The face marking is a little tougher; if the horse will tolerate it, clipping will help, but you need to be extra careful to blend the clip line - if you've never done this before, do it AT LEAST two weeks before a show. The powder trick works here too, but you have to work slowly and carefully to avoid getting it into the nose or eyes. Dampening the powder a little and rubbing it into the hair a little at a time is the way to go.
BTW, the blade in a standard ear or face trimmer runs between 30 or 40, too close for this kind of work - you'll scalp the poor horse bald. You need a clipper that will take a variety of blades, and a 10 blade works best.
Last edited by maura; 03-09-2013 at 02:21 PM.