Getting cast

My little Shetland filly keeps laying by the fence. I've had to go roll her over so she can get up a few times now. She's not in a stall, she's in a pen outside.
She has plenty of area to lay down, but lays by the fence.


How could I stop this? One day I might be gone and she could be stuck for a long time.

Do you have any old, cleaned off, wooden fence posts your could lay right next to the fence? How about an old water tank--I would put that upside down or sideways next to the fence.
How about some old, moldy straw or hay bales? She won't eat them--horses are too picky.

Pretty sure I could get ahold of those things