Oh yeah, they can still detect it, it can be as well hidden as you want but they are going to smell it regardless. The only way to keep them from detecting would be to use something to throw off the scent like coffee grinds.
And OxyContin is an opiate, they will detect it. I'm not sure if they are able to detect synthetics like Fentanyl.
It would be pretty nasty, but hiding it in meat could be a good place. Definitely wouldn't take anything after hiding it in meat.
