Can a spayed male dog still get a female pregnant?

Speaking as someone with a neutered male dog who has recently decided that he and my spayed female dog should be...er...more than friends...boys will be boys.

If there are male dogs around with easy access (kept in the same fenced in yard or house), they're going to know she's a female and get a hankering to "show their affection" once in a while. If she's not in heat, though, which she won't be if she's spayed, she won't be attracting random strays from the neighborhood.