As someone who you could say... works in the field (don't worry, don't give a shit about quantities one would encounter at Glastonbury), it's this. Pretty much every single hiding method is known. It's all comes down to pure luck, how much shit is given about finding the substance and general randomness.
Does anyone care about bringing in a few tunneled out (not hollowed out completely!) watermelons? Few doughnuts with some favors baked into them?
P. S. Almost forgot... Frozen tuna is another great way to bring shit in or so I hear!
P. P. S. Yes, average cop knows about your weed in your ketchup bottle, some blotter taped under your boob or some pills under your foreskin. It just comes down to how dedicated they're to finding that stuff.