Simple but lasting subterranean animal barrier - ferrocement?

I am working on in-ground, outdoor, colony-style rabbit systems for the sahel. One of the primary challenges is keeping the rabbits from tunneling out. Bricks is an obvious solution, but end up being fairly expensive (~$100 for a 2x4m rectangle at 1 m depth). I'm looking for alternative ideas that would be cheaper, but wouldn't rust or rot away in the first few years. Structural integrity is unimportant - it must only be able to withstand rabbit burrowing.

Any ideas? A thin ferrocement is the best I've come up with so far.

Available local materials include:

sand
clay
laterite/lateritic rock
cement
plastic rice bags
chicken wire and similar wire mesh

Wood and steel are available but expensive. We have a 9 month dry season so a water-based barrier is out of the question.

Thanks! (And sorry if this is the wrong forum for this question!)

Sounds like you have options! I would think cement reinforced with chicken wire would work. So would cemented rock. If you have glass bottles, you can use those as bricks too.