for the mud monsters I let the mud dry and then metal curry comb it off (be careful!!). There will be alot of dust but it will get the chunks out. Then rubber curry in circles really really well and use brushes in order from stiff to soft. It takes time but will help alot. Be careful on the legs and use rubber curry on those. Do not metal curry on legs!! After brushing you can bathe or just rinse your horse. You don't have to but it will get any remaining dirt out.
Finger nails also work really well if your not afraid to get dirt under your nails just giving the horse a good scratch where he/she is itchy(or not) and Bam the mud gone. :)