From Longman Dictionary of Contemporary Englishbelt and bracesbelt and bracesBritish English informal a belt and braces way of doing something is one in which you do more than necessary in order to make sure that it succeeds → belt
Examples from the Corpus
belt and braces• Where glues are concerned, I, personally, would not scorn to wear both a belt and braces.• It retains the Sympatex lining of the earlier model - belt and braces if you like.• It was sealed with Sellotape and staples, a real belt and braces job.• Three: portly old men should use belt and braces, in case their trousers burst open; the belt hides the disaster. 