well, like with every form of birth control--patch, pill, barrier, or natural--you have to be consistant. if you're not consistant, then you'll likely get pregnant.
we switched to a lubricated latex after using nonlattex for a while. we thought that we were having a latex reaction, btu it was really a reaction to spermicide. so, we dont' use spermicide--just condoms. it's worked for us for the past 7-8 yrs; and i've only been doing FAM for the last four-five months.
i don't want to get pregnant either, that's why we're not cavelier about these things. consistancy is the key.