If the pool are in an open area, or where the cage can be subjected to high winds, then consider either a low profile enclosure, or one that is secured to the ground by the tracks. You can find retractable pool cover via http://www.automaticpoolenclosure.com/covered-pool.html.
Is your pool surround (either paving or decking) in good condition? Is the level and solid? In order for the pool enclosure to work easily and efficiently your paving should be as level as possible and also paving should be smooth enough, especially if you do not have a system to track.
If you have chosen to be tracked then the system is not so important. But if you surround a very uneven, you may need to consider repairing the boarding level, or even off the platform.
Subtle surround the swimming pool, the easier the enclosure will operate.
If your coping stones are raised above the surrounding pool area, you will need to take this into consideration when taking a measurement of your pool to the enclosure. This also applies if you have a raised lip around your pool. Generally many people would like to have the cage to sit tight as possible into the pool, if there is limited space, so that each measurement must be at least 10 cm beyond copings lifting ensure cleaning their cages.
This is often the most difficult decisions when choosing an enclosure. The fundamental difference, from a user perspective, between the two, is the ease of operation. A tracked enclosure can be easily and quickly opened and closed with just one person, whereas the trackless enclosures generally require two people. This is due to the fact that the enclosure module needs to be pushed, or pulled evenly on both sides to avoid the whole enclosure moving offline.