It is not simple, nor is it cheap, to put a sturdy and safe fence around a pool. No way would I ever foot the bill for that on a rental property.
This is a picture of what the state I live in (Queensland Australia, which has very strict pool fencing laws. In fact a house with a pool can not even be rented out without meeting these laws) considers to be an adequate pool fence. It has to be at least 1.2metres tall, have no horizontal peices that are at a height that could possibly be used for climbing over the fence, and the gate has to have a magnalock that is key lockable, and that lock/latch has to be at least 1.5m from the ground. (it's usually part of a pole that extends above the gate height)
For an idea on pricing, one 6ft long and 1.2m high panel of pool fencing (not including the posts or cost of setting those in concrete) is about 100bucks from avg pool stores here. (Granted that's Austrlian) .. so you would be looking at 1000's of dollars here, and probably not much less there.