Probably in the sand bed. Mine hid for about 3 days when I first introduced her. Don't be suprised if you don't see her for a couple days. The biggest issue with leopards is acclimation. If it makes it past about a month they're good from my experience. I've had mine about 3 months now.
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20 Gallon SPS reef
29 Gallon FW "fat catfish" tank
20 Gallon Long Dart Frogs "Zig" and "Zag"