I have a bay and his favourite thing to do is roll. Especially after rides or when i wash him. I would suggest you let them dry before letting them back into the paddock so the don't get dirt stuck to them. If your paddock is muddy there isn't much you can do unless you want to rug them. *DO NOT WASH YOUR HORSE TOO MUCH* i know its tempting but don't! Too much washing with shampoo can be bad for the horses skin. Wash them every now and then but be careful not to wash the too much. Brush them lots and lots. A main cause of rolling and getting dirty is being itchy! So lots of rubs and brushes with help. Hope this was helpful!