One of the most unfortunate situations that I see everyday with leopard gecko owners is that because an adult leo can live in a 10 gallon aquarium, they all do live in a 10 gallon aquarium. But with a pet that can grow to 10 inches long, a 20-inch long length means that they're living in a tiny little environment and don't have much room to move around. Clutter it up with a bunch of hides, bowls, and other necessities, and you have a gecko that really lacks room to explore, stretch out and live a happy life.
This was really made apparent to me when I moved a leo who spent the first two years of his life in a 10 gallon into his new 20 gallon long tank which nearly doubled the space he had to run around. I saw a much more active gecko, a much more secure gecko (evidenced by the fact that he often sleeps outside of his hides, in the open), and if I can presume, a much happier animal.
But what if you don't have enough room to hold a larger aquarium? What can you do to make the 10 gallon a little more comfortable for your gecko? Here are some ideas you might appreciate.
The easiest thing to do is to add a second level to your leopard gecko habitat. If it covers the entire space of the aquarium, minus a ramp for your leopard gecko to climb up, of course, you've practically doubled the space in the tank, and provided a big new hide that can function as a warm hide for your gecko since they'll be very close to the under tank heater. Add a little bit of dÃ©cor to the top of the aquarium, and your humid and cool hides there, and you've got a clutter-free space for your gecko to just hang out.
There are a few concerns to making a large second level, so you may just want to construct something smaller, perhaps a simple hide that is long and flat, allowing you to add a second-level hide or a water bowl, plus some free space. A fall from a high ledge is not a good thing, and neither is being too close to a higher-wattage heat lamp. You also don't want to put them too near the leopard gecko lighting for the same reason. Even a small, three or four inch tall second level is a big improvement, since it allows you to stack things that would normally take up more space.
Depending on how high the second level is, and the type of heat source you use, you could even include both warm and cool hides on the same side of the tank. In one tank I have added the second level on, with a UTH on the bottom and no heat lamps, I was able to get the temperature up to 89 degrees on the bottom level, and 81 on the top. While neither is really an ideal temperature for a leopard gecko to have, it works very well for the leos who live there, and I was then able to basically open up a large area in the small tank.
There is the question of what your gecko would do with an open area. As someone who has over 20 leopard geckos, in all sizes and shapes of aquariums (no rack for me), I can say that some of them use the space, and some don't. I have a few who simply sit out without a hide at all, laying stretched out in the empty space. One of my leopard geckos will wake up every once in a while and pace back and forth. Most of them use the space as a way to make hunting crickets a little easier. They can not only see the crickets much better in open space, but they don't have to crawl on or around furniture, attack at awkward angles, or wander around looking for them. The biggest advantage that I see for a second level and an open space is that it simply allows your gecko more room to explore and wander.
If you insist on having more decorations, that's all well and good too. You should be able to add at least one or two extra pieces to your 10 gallon with a second level, even if it only covers half of the tank.