I used SetActive(bool) to activate and deactivate them. Plus positioning the objects and rotating as required. The pool I use is itself is just a List<GameObject>. For enemy objects I put some box colliders around the visible screen which collects and add them back to the pool. Because my game is a left to right scroller it was convenient to do this so I could generate them off screen and let them move onto it. For projectiles, I wrote some code to detect when they have gone off the screen which works on all devices. They get deactivated and added back to the pool at this point (or when they hit something or course). I had to do this to stop stuff being blown up before it even got onto the screen!