HerRoom Response: Your band size is probably too large. If your band is moving around your body, this friction wears down the casing covering your underwire and ultimately causes a hole for the wire to pop out. In a really bad fit, this hole can occur within a matter of hours. Try a smaller band size and a larger cup size (e.g. go from a 42D to a 40DD) and see if your bra stays in place better.
Marg from Detroit suburb, MI, USA