If your schedule has you gone often where you could not be a daily caregiver for the child/children, then you could agree to the mother having sole physical custody, but you still retain joint custody - meaning that certain decisions have to be made by both of you, she couldn't just pick up and leave the country without your ok, medical decisions made jointly, schooling, religion, etc...
As far as visitation goes - well that can be decided between you and the mother too. Examples - 2 weeks in the summer, every other major holiday, 1 week in the spring and fall, etc....
Visitation can be very tricky I'll have to say. I have a friend who had a not so great divorce and his ex-wife often does things to mess up the visitation rights (one side of the story of course - there is always a rebuttal isn't there?)
USMCFLYR