@Karin Givon you can't get a deleted card back and there's no way to stop people with edit permissions on the board from deleting them.
You can backup your Trello board periodically using the API, here is a google apps script solution for that:
You can also see in the board activity who deleted a card, so if someone does do it you can tell them to cut it out, but there's no way to protect against malicious action or incompetence resulting in deletion of a card other than to back it up and tell people not to do it.
If you had to thrive a new habit during a lockdown, what would it be? Trello
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