Your using this type of ladder guard ?

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https://www.amazon.com/Polaris-G21-Inground-Swimming-Pool/dp/B0087N73HU/ref=sr_1_4?keywords=pool+ladder+guard&qid=1560622918&s=gateway&sr=8-4

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Ive seen a a pair installed on each side of the ladder to keep it out.

Another solution could be to use the ladder hinges meant for auto covers that lift the ladder out of the pool when the cover closes. You could lift the ladder out when not in use

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https://www.royalswimmingpools.com/ladder-hinges-apc-pair.html