We have done dig boxes for our ferrets in the past, with great success.
We got a 50-ish gallon plastic storage box and put several dozen pounds
of potting soil in it.  They loved to snorkel under the dirt, and the
dirt comes off their coats easily.
 
Another one we did was a rice and bean box.  You can buy large bags of
rice and beans for a minimal cost.
 
We also did a small child's pool with some water in in, and put alot
of their plastic toys in it.  They enjoyed fishing for the toys and
occasionally putting their heads under water.
 
The plastic ferret tunnels are a constant source of entertainment for our
brood as well.
 
Hope these ideas help!
 
Becky and Heather and the Excellent Eight (formerly the Magnificent
Seven): Abby, Andre, Annie, Farty Pants, Bob, Sleepy, Peanut and
introducing...Egan!
[Posted in FML issue 4392]