Question about colony rabbit burrows

I decided to stay away from the mesh floor and give my rabbits some more room.  They have a 120 sq ft pen.  I tried artificial burrows with large trash cans but they wont use it,  and the largest house pvc tubing to make entry holes is too small for the rabbits(and larger pvc pipipes are too expensive). Its a very large rabbit breed. I’ve also tried cinder blocks and wood but the wood got eaten and the cinderblocks didnt keep the nests drie... So i was thinking throwing a large pile of dirt and letting them make their own burrow.  I’ve seen some other people do it.  My concerns are catching the rabbits for processing,  and what if one of the older rabbits dies?  In nature they get eaten usually before they die,  but dince that wont happen in my case,  what if it dies in the burrow?

I've let my rabbits breed and burrow naturally in the ground.  It's an awesome low-fuss way to keep them and the outdoor temps never phase them.  They dig 'cooling runs' in wet areas, big enough for a couple adults to go down and cool off in the summer heat.  They dig 'oh s**t' runs for quickly disappearing from danger, and they dig birthing burrows.  But you'll likely never find that burrow.  They hide them very well; basically they collapse and pack-in their nursery tunnel every time they leave, and dig it back up every time they enter, which should be once a day.  Sometimes the entrance is obvious, but the burrow seems to dead-end just 12" in.

The thing is, rabbits like to burrow 1-2' deep and several feet across, from what I've found (I've dug up a lot of burrows).  So you need a lot of dirt.  And don't think the'll leave it in a pile.  They will spread it FLAT if you let them.  If you want to provide an "above-ground" burrowing area, maybe make a cinder block retaining wall at least 24" deep and at least 5x5' in size.

The other thing that comes to mind is I have had issues with does fighting over best burrows.  Even when they had a 30' diameter round pen with water feature, and a greenhouse in the center, filled with straw and hidy-nooks, the does would often dig up one anothers' litters and kill them, then have their own litter in the stolen burrow.  This is the main reason I stopped raising them this way (for now).  Granted I had like 9 does, and I've learned over the years that doe chemistry is very sensitive, and some does just HATE each other and will never stop fighting or killing the other's litters.  So I was dealign with some bad social dynamics.

There's no micro-managing litters. You won't know they're born, or how many there are.  If you know your does' behaviors and watch for lactation, you may know for certain they had a litter, but otherwise you might just come out to see tiny fluffy puffers hopping about the run one day. I believe when kits die in the burrows, their bodies kind of sink to the bottom of the nursery chamber and get lost in the litter. It's so cool underground that they don't really 'rot' enthusiastically.  When the litter is grown, the doe fills in the nursery chamber and will dig a new one or clean out the old one for the next batch.  So I don't think kit deaths are something to worry about.  I've also never had a rabbit choose to die inside a burrow.  But then, I haven't had many adults die.  

As far as catching kits?  They're way more skittish, usually, then rabbits raised above ground.  I get 'em hooked on treats that I feed in a big wire dog kennel.  Every day I feed the colony treats in the kennel and hang out. When I need to catch a rabbit, I use a long string tied to the door, I stand far away and wait for the kennel to fill up, then snap the door shut behind them.  

Age for catching:  I found that 'teenage' rabbits raised underground ar a PITA to catch.  They're so 'predator savvy' and might learn early on about the trap door on the kennel.  I've had rabbits that refused to enter the kennel passed a certain age (usually the boys).  So I started catching fluffers when they were young, before the wily teenage time sets in, and grow them up in another outdoor run without any burrows in it.  It tames them up a bit and makes them way easier to manage and catch once they're adults.  Plus, I don't have issues with watching my breeding colony and being like "Woah, hey, which rabbit is that?  How long has it been in here?!  WHY HAVE I NEVER SEEN IT?!".  I've seriously had some buns that became so skittish as sub-adults that I never even knew they were in the run!   That's why I take them out before they have a chance to get that fast and smart.

Edit:  If you have ,say 4 breeding adults, and one day there's only 3, and you suspect it died rather than escaped; if you have a carefully contained raised bed for burrowing, it shouldn't be difficult to dig it up and search for a body.

That said, I've also had somewhat good experience using hay bales.  I put them on their side (lengthwise but with their tallest side upward) and made littler 'chutes'.  Then covered the top with wood and the back with more bales.  The rabbits LOVED it (they were above ground strictly at that time).  The kits stayed cool in the straw.  Though I had issue with kits wandering from the nest and dying, and also not detatching from mama while nursing, and getting pulled out of the nest (which rarely happens with burrows because the does is dragging them uphill and they get pulled off, then she seals them in so they can't wander out and get lost).  Also, the bales only last so long.  The does tear them up for nesting materials and sometimes burrow holes through them- then seal that hole, burrow a different hole, seal that hole, etc etc.  But, it did work well and was a fair replacement for underground burrows as far as temp control and doe happiness.