Disclaimer: I have only 2 tokays, my experience lies more with other gecko species (cresteds, gargoyles, panthers, vorax)
That out of the way, I keep all my adults (and many of my juvis) on a bioactive substrate made up of organic potting or garden soil. I used to mix some with sand, but I did not see any benefit to it for my plants or geckos, so I just stick to the organic soil. In the past 8 years, I have not had a single occasion of impaction from this, but my geckos don't really hit the dirt to eat. I also have a layer of leaf litter in some of my tanks, but not all (no real reason other than I was too lazy to go get more leaves and sterilize them when I set up the other tanks). Food does hide in it, but my geckos are all nocturnal, so it doesn't really matter as the bugs come out at night again). Some bugs will breed in the terrarium, but it's rare, and the offspring are quickly eaten. On those rare occasions that the big bugs do last more than a few days, I toss them back into the bug colony so they don't stress the lizards too much.
If you go the bioactive route, make sure you add a drainage layer, and screen over the drainage layer so the soild doesn't mix with the pebbles/clay balls. also be sure to remember to turn the soil - first every 2 weeks, then can be done monthly. Also remember to add isopods to help keep things going. there are several good tutorials on how to build a bioactive substrate both in written form and on youtube (I like the videos Mike does at New England Herpetoculture)
Good luck and enjoy the process of building
(It's one of my favorite parts)
