Mine have never burrowed, but I know that they can. Checking the filter is also a good idea when you can't find a kuhli. Keep any intakes covered well for this reason!
I'm thrilled to say that I have kuhlis that are out and about 24/7. I have a few tips that I like to hand out for this!
- More kuhlis. If you think you have enough, get a few more. While kuhlis aren't necessarily schooling fish, they are very social. They enjoy the company of one another immensely and will be much more comfortable in the tank if they have lots of friends. I would personally consider 6 to be the bare minimum. Also, you may or may not have luck mixing different Pangio species in terms of them hanging out together. I've heard it go both ways.
- More hiding spots. If you think you have enough, make a few more. It sounds counter intuitive, but the more hiding spots you provide them with, the more you'll see them. They know where every safe place is and thus feel more comfortable being out in the open, knowing that they can retreat to safety whenever they deem necessary.
- More plants. If you think you have enough, get a few more. Kuhlis love draping themselves in plants and scavenging around them. Floating plants are excellent as well. If you can, arrange plants in a manner that creates an area of lots of shade from tank lights. I prefer live plants. I'm not sure that I would go with plastic here, as they could very easily cut themselves. Silk may be alright as long as all wire ends are tucked in.
- Water changes, water changes, water changes! They love fresh water. Nothing brings on the kuhli dance like a like a 50% water change.