How long have you had Leon, how old is he and how big? also, what size feed is he on?
Sometimes snakes will extract every last piece of goodness from their food so there is very little left to er, come out the other end.
If there is a noticeable bulge infront of his vent then he could be constipated. Warm hands when handling or a warm bath (make sure you measure the temp with a digital thermometer, so its around 25-27c) usually helps to get things moving.
Also, make sure you have a really good look around the viv, as sometimes it will be very difficult to spot. Mind you, you should be able to smell it before you see it!
9.11 Cornsnakes 1.1 Hogg island boas 1.0 Dwarf Burmese python
have you handled him much in this time, because often handling the snake can prompt them to poo! i know Blaze always poos after ive held him about 10mins or so!
1.1 Cornsnake: Fluffy and Blaze 1.0 Kenyan Sand Boa: Falcor 0.1 Bearded dragon: Chilli 1.1 Cats: Jackson and Mia 1.0 Fiance: Ade :)