[NickRandom]

The perineal favorite is Vicks VapoRub daubed copiously on the top lip just under each nostril.

There isn't much that can overwhelm that solution although something like a liquefied sealed body bag that's been stewing in the sun for a few days does manage to seep through when first opened.

[giantg2]

Not sure why you're downvoted. Vick's under the nose does drown out most smells. And the decomposing body comment is on-topic, as this is a trick that is common in law enforcement and medical roles.