Honestly, with only 10g, I'd consider a smaller species, a fish, or an invertebrate. However, if you do choose to go with leopard geckos, perhaps try to get as others have suggested a tank with a 10 gallon capacity but a larger floor area; many reptile expos sell tanks that are essentially a 20 long but cut down to have only a 10g capacity. You could only keep one either way as they're not a terribly social species and would definately fight in confined quarters. Just remember, that 10g tank needs to somehow fit 3 hides (one dry and cool, one intermediate, and one warm and moist), a suitable temperature gradient with a good 10 degrees difference from the hot and cold side, a water bowl, and a calcium dish. Also, never use sand, even the so-called "digestible" sand, since leos are notorious for eating the sand and getting impactions. Feeding out of the tank is also advised to prevent consuming any of the bedding, even if it is just paper towel.