I'm sure you know, but do watch out for anything that might be poisonous if he's at the putting-things-in-mouth stage! RHS has a useful list of common garden plants that can be poisonous here: http://www.rhs.org.uk/Gardening/Sustainable-gardening/pdfs/c_and_e_harmful

Not to say you have to uproot anything that might be bad for Leon, just put it where he can't get at it (like behind some chicken wire or netting).