It would be interesting if you could do a side-by-side comparison of expired and 'fresh' cannister, using a variety of metrics. In other words, see what expired really means if anything.

Save all of your old cannisters. I wrapped each in a section of nylon stocking with each end tapped closed. I dip them in bacon grease. Each is them stored in a zip-lok bag for later use. The can is quite thin. Most animals will bite thru it. I place three or four around our camp. It picks up bears, skunks, raccoons and stray dogs.

Nothing works better for the neighbors dog in your trash can.

I like that idea,Alot!Maybe I'll think of something to keep the pilferer's out of my Blue trashcan,here in the city -

I'd take pepper spray over empty hands or a contact weapon, which makes it potentially useful in nonpermissive environments where I cannot carry a pistol.

IANAL but the general concept of self-defense does allow you to "strike" first if you think serious harm to you or someone else is imminent, so you aren't necessarily in the legal wrong. Especially if you then escape and report it promptly, there's little to indicate to the police or DA that you intended to assault the other guy, if the other person claims that.

Alas, real life is rarely so neat and tidy.

From a legal standpoint, the limited range of pepper spray or even a Taser can be an advantage. It demonstrates how close the other person was when you engaged them and it bolsters your legal claim of self-defense from imminent harm. Of course, tactically, distance is your friend, as NightHiker said, so it's a tricky trade off.

Anyone have any thoughts on the merits of pepper gel or foam?

Seems that foam has less reach, although hitting the eyes of a moving target may be easier. I hear the argument that the assailant could scoop the foam from their face and throw it back at you, but if you're not standing like a statue yourself, that may be an unlikely outcome.

Gel seems to have a lot of merit. Less blowback/crosscontamination for indoor use, more range than foam, and less chance for the guy to throw it back at you.

Granted, one huge component largely missing for either gel or foam is the potent respiratory effect that a cone or fogger, in particular, could inflict on someone if they breathed in the aerosolized droplets.