Don't harvest/cut the spears for the first few years (most say 3 years). Let them bush out so that the roots/crowns develop a bit. Then they'll push up more spears the next year.
You could dig them up and separate them, but I don't think that'll help them spread faster. It may even stunt them.
I've never had issues with anything eating my asparagus. And I've had issues with groundhogs, mice, rabbits, squirrels, and birds with other crops/plants. I can't speak to deer though (no experience with them somehow).
Weeding is important. Keep the competition out as much as possible.
I'm moving to a "Back to Eden" style mulching this year. I just put a thin coat of wood chip mulch on the asparagus. Anyone have experience with BTE and how it relates to growing asparagus? How thick is ok for the spears to push through?
CharlesH - I'm jealous! Fresh asparagus are among my favorite veggies! We have a small plot and have enough for about a 1 meal a week (for my family of 7). I'm currently cutting about 8-10 spears a day.