They ADORE horse poo!!!
They all do, Mari, they all do.
The screen thing works a treat, though. Papa made Gran's out of the smallest chicken wire and 1x4''s, in big 8 foot squares that he then used cross pieces to nail together to cover the whole garden plot; the flower bed screens were custom fitted to each bed. Gran always edges her flower beds with bricks or cinder block or lava rock, or something, so it made it easy to weight the screens with the big, heavy cinder blocks on the edging.
We always had little chia-rat dogs, but my aunt didn't; and Chico the Enormous was parTICularly fond of horse poo--if he saw a wheelbarrow of it out, it looked like he'd found a tub of ice cream, the disgusting creature. But the screens foiled him every single time. If you want to compost your beds over the winter with poo/straw, I think that after a few hours of not being able to get to the poo, the boys would give up.
The hard part is getting rid of the covering straw in the spring in order to plant the beds. Nasty, decaying, old poo stinky straw....Just how bad do you want pretty flowers??