horses are fond of pulling out hay to make beds and bathrooms

I gave up on round bales for that exact reason.  I tried the rings, but then they rubbed off thier manes or or else my gelding will try to climb inside and get stuck. 

We had the same problem with the horses rubbing their manes off on the hay rings.  There are rings designed for horses but they are quite a bit more expensive than those made for cattle.  Our solution:  a friend with a cutting torch removed the top section of the cattle ring.  The ring is now about waist high.  High enough to keep the horses from pawing the bale but low enough that they don't stick their heads through it.  It also makes the ring much easier to move around.

As far as the hay getting "nasty"...the horses will eat the center out first.  That's where all the good stuff is.  They will not eat the nasty stuff unless they are given no other choice.   Would you eat a moldy piece of bread if there was fresh bread available?   So, once they have eaten the best of the bale, put out a new one and let them make a bed out of what's left of the old bale.   Do not force them to "clean their plate" so to speak.

RIDE ON!

In my experience most horses won't eat bad hay, that is unless they have no other choice.  Like above, they will tunnel into the center through the flat sides finding the best hay.

I have seen round bale feeders that have "legs" and hold the hay up off the ground but I can't testify to their efficacy.

My big issue with round bales is the nasty muddy slop that forms around the ring which the horses stand in while eatting.  Better watch them for signs of thrush and white line disease.

Everyone has offered really good info on round bales and I agree with all the info.  I'm choosing not to feed round bales and didn't last year either.  I agree it makes your life a lot easier, but not always.  My situation is a dominant mare that tries to control the round bale, an older gelding that doesn't have an "off switch" when his tummy is full and a couple of younger horses that are just trying to fit in.  I chose to feed square bales last year and this year for the above listed reasons and it's working out a lot better for my barn.  I can throw a bale in the mornings an hour of or so after they have had their breakfast and it will last all day.  I can throw another bale and hour or so after they have had their dinner and it will last most of the way through the night.  I scatter several big flakes of hay in the paddock and they play musical piles for a few minutes with the dominant mare controling the movements until everyone settles down.  The older gelding gets enough hay, the dominant mare gets bored with trying to control everyone and life is good.  I guess you can tell that we don't stall our horses unless it is needed.

Happy trails.

Almost the same as my deal except insert pony for two young horses. Also I choose to feed the square bales because I take it into the field with a fourwheeler and can put it somewhere different every time. Lots of the time I take it to the far corners in the rear of the field. No mess.