Can Your Horses Sleep Over?

I live on an acre of land and am not good at plowing down the weeds, or should I say "natural grasses" that thrive here.  So I am always grateful when someone asks if they can bring over their horses to eat their way around the house.  Currently I have a friend's two horses right outside my house plowing through the weeds for me.  Last night at a meeting I heard that the rye grass was only about 18 inches tall in our city.  Not so at my house.  The rye grass is over 3 feet tall here.  So you can see why I am always glad that friends will allow their horses have a sleep over.