I carry a hammerless S&W 2", 5 shot in my back pocket in a leather sleeve. Ankle holsters are hard to get to and if you have to run, you stand a fair chance of losing that gun. I use to carry two backups and I put the other one in my vest.
If you end up in a situation where you are going to need to use your backup, it will likely be because you are in a fight for your life and if that is the case, you will probably be making a contact shot. But many different scenarios are possible.
If you have someone on top of you and your backup is your only option, you want to be able to easily get to it. Same goes if you do not have someone on top of you. Try to think of every possibility when you make a decision onn where to keep your backup and what type of gun to use.
"If you expect logic associated with California law, it will only make your head hurt.." - Ron-Solo, 2013