In warm to hot weather, dunk 'em in the stock tank. You gotta hold the dog in for a bit, head up, of course, so as to not scare the bejibbers outta them. That's what moose do to get rid of ticks, soak in a lake or slough.
In hot weather it's great for you too.
To make it easier on the person, me, I'd take them for a loooooong walk thru the creek, lengthwise [is there a preposition to describe that] I'd keep moving across side to side to stay in the deep part so they would be mostly immersed.