Fault attacks consist in changing the program behavior by injecting faults at run-time in order to break some expected security properties. Applications are hardened against fault attack adding countermeasures. According to the state of the art, applications must now be protected against multi-fault injection. As a consequence developing applications which are robust becomes a very challenging task, in particular because countermeasures can be also the target of attacks. The aim of this paper is to propose an assisted methodology for developers allowing to harden an application against multi-fault attacks, addressing several aspects: how to identify which parts of the code should be protected and how to choose the most appropriate countermeasures, making the application more robust and avoiding useless runtime checks.