A 3' fence is not code. 4' is code.

again, we have a 4' fence around the yard
the baby fence is for inside the yard, to separate the pool from the rest of the yard

re: 3' not being sufficient --> please explain why 3 feet is insufficient.
my thinking is if they can climb a 3 ft fence they can climb a 4ft fence no?
also, by the time they can climb a fence they should be swimming like "fish" anyways?
also, we'd create a strict set of rules regarding the pool area and no fence climbing would be part of those rules.

ultimately, isn't conscious supervision is the most important thing?