NO, don't do one at a time. If possible, have enough traps to try and trap all at the same time. If you have 4 cats, setup 4 traps. Once one goes in cover and remove immediately! You might check with feed stores, rental places, Humane Society, etc. and see if they rent traps out.

Here's a link to the group we work with, which might give you more information:

www.azcats.org

(we're listed on the home page for getting an award from the City for TNRing, and for Cat Fancy Magazine doing an article on us).