Your decals should not fall nor fly off when driving in normal nor inclement weather. Though it is critical to place the decals in a good position to help ensure that this doesn't happen. Decals should be placed on smooth/flat areas of your car. They should not be placed on paneling or cracks. With any type of car decal you should not use a pressure washer or a mechanical car wash. The water pressure and large brushes of either of these can damage your car decal beyond repair or even cause them to fall off.