Our BCI's love a good thick layer of aspen to root around in and burrow in, sometimes they are totally buried in it. With Rauri as she was so big I mixed a 2/3 cypress mulch 1/3 aspen for her. We used the double milled cypress as the single milled had some huge and pretty sharp hunks of wood in it. It gave her lots to mess about it but the cypress held up better under her greater weight (the aspen just compacted too much I found with a 6 foot snake's weight lazing about on it).