I just read that page over, you have great top soil there, no fertilizer and it contains peat moss, a natural "humidity sponge"

toss a little sand in there and stir it up good, and you will have a nice breathing soil that should hold a burrow well.

Best wishes.
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Regards,
Wayne A. Harvey
Thamnophis US
Thamnophis.co
Thamnophis dot net

too many darn snakes to list anymore...