When you're trying to give a leopard gecko a home in captivity where it'll be happy and healthy, the starting point should of course always be to think about its habitat in the wild. In the wild, the leopard geckos habitat is the desert areas of Afghanistan, India and Pakistan.
Does this mean that every leopard gecko terrarium should contain sand? Well, no. A common mistake that people make is to hear that these geckos live in desert regions in the wild and to think "desert = sand. It's hard to shake the visual association of the word 'desert' with 'endless shifting sand dunes,' but the fact is that only about 20% of the areas of the world that are classified as deserts are covered in sand. 'Desert' means 'dry,' but it does not necessarily mean 'sandy,' and the desert areas where leopard geckos live in Asia are characterized more by rocks and grasses than by sand.
This is probably the major reason why sand remains a popular substrate for the bottom of the leopard geckos terrariums, despite its known health risks. Then again, it's not the only reason: many leo owners would probably still prefer to use a sand substrate even if they knew it wasn't a natural environment just because it looks good. It's hard not to have a little sympathy with this position, because you could argue that it doesn't matter whether a pet's environment in captivity is natural, so long as the pet is happy living in it. After all, what's 'natural' about human beings living in cities?
However, for those who want to approximate a natural environment for their leo without sacrificing looks, there are two other options worthy of consideration:
1. Slate Tile
A slate tile in the bottom of you leo's terrarium looks good, is very easy to clean, and approximates a rocky habitat in the wild pretty well. If you want to, buy a selection of smaller tiles in different colors and patterns and mix-n-match them to create a more interesting visual. Add fake rock features and plants for an even more authentic look.
2. The 'Full Natural'
For those with the time and the will, the five-star habitat option for leopard gecko owners is something that truly replicates the leo's home in the wild. Start with a large tank, at least 20 gallons (ideally 40 gallons) for one leopard gecko - this is necessary, as creating a natural environment means more of the floor space is covered, meaning less space for your leo to run around on. Put a one-inch layer of a mixture of equal parts peat moss, potting soil and play sand into the bottom of the tank as drainage for the plants. Then add some plants (you'll be able to find lists of plants which are reptile-safe on the internet). Next put in a layer of sand/soil mix, then add rocks, logs, and finally fill any gaps with more play sand.
(NB: If you haven't heard of it before, 'play sand' is a washed sand that's produced for children's sandpits. Because it's clean and very fine it greatly reduces risks associated with geckos ingesting it, particularly when it's used sparingly.)
Either one of these two suggestions is going to give your leopard geckos habitat one that is worthy of this amazing lizard.