Use a non particular substrate such as non-stick shelf liner or plastic table cloth. Spot clean every poo you see every day with anti-biotic soap on a wet paper towel, then wipe dry. Pick out any uneaten food every day as well though greens don't have much of a smell if dry. Add a little chopped parsley to the salad mix (when cut it gives a nice pleasant odor, don't have a clue if this would improve the smell of the dragon's poo LOL but might cover a bit).
I have never noticed any smell from my dragon, when I cleaned every poo as soon as I see it, even if I don't clean the entire cage once a week. Actually with spot cleaning I just did a complete cage clean once a month without any health problems with the dragon.
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PHLdyPayne