My view is that if he is climbing, then it is time to take the sides of the cot. It is a long way to fall over the top of a cot and he could hurt himself. My kids both went into a toddler bed about that age and as elf angel said, we put a stairgate on their bedroom door and made sure that their rooms were safe for them to be wandering about in, and left them to it.
I guess it depends on the child, but ours never tended to get out of their beds at all until we went into them, they just used to lie in bed and sing or shout until we appeared - that lasted until they were about 5 - obviously we didn't have the gate on their door by then, but they just never ventured far!!