The phrase "foolproof method" means a way of doing something that is extremely easy and simple, so even a foolish or careless person could do it without making any mistakes. Full definition
For a wife to nag her husband to go to AA is an almost foolproof method of keeping him away. (religion-online.org)
Even if your building features top - grade security, there's no truly foolproof method for keeping CA thieves outside when they're truly intent on getting in. (rentersinsurance.net)
Although not necessarily ideal from a security standpoint (as you may not wish to share your Wi - Fi password with the guests you want to share your Chromecast with) it is currently the most foolproof method as it works across Android, iOS, and desktop operating systems. (howtogeek.com)