Is there a very stinky chemical solution that isn't a health hazard?
My vote would be for butyric acid and related short-chain fatty acids with between 3 and ~8 carbons (isobutyric acid, valeric acid, isovaleric acid, caproic acid, etc.)

In pure form these chemicals would be dangerous acids, but in dilute aqueous solution buffered at pH 5 or so, they are not very corrosive or toxic but are still pretty stinky.

Skatole could be another example.  See the Wikipedia article for malodorants for some more ideas.