One of our guest hikers pulled out a bottle of unscented ammonia, poured some into six half-pint containers and set them around the kitchen, including some smelly stuff. Nothing was disturbed overnight for all seven days on the JMT.

Q: Is ammonia an effective deterrent?

You might have been able to set out six half-pint containers of water and nothing was disturbed. That wouldn't make it an effective deterrant, either.

--B.G.--

"That wouldn't make it an effective deterrant, either."

Nor would it mean that it's not an effective deterrent.

A quick google search shows a variety of sites promoting ammonia (usually rag-soaked in a dish of ammonia) as an effective deterrent for squirrels, possums and raccoons, among others.

Maybe it's like urine

If you mark your site with urine it might keep away critters

Critters sometimes mark their territory with urine

I sometimes mark my site with urine - maybe a Cougar or Bear would smell that and go a different way, rather than walk up to me (sleeping) and be surprised