You might try "stretching" the hem, sometimes that helps to pull the offending cord/wire back into the stitching. It comes out because the weight of the garment will cause the whole thing to stretch down, lengthwise. This causes a narrowing of the width, especially in areas that are hanging on the bias. You just need to stretch them back out width wise. I have a very full bellydance skirt that has fishing line in the hem to stiffen it and make it stand out. It frequently tries to peek out. Tugging it back in usually works. If it hangs out too far to pull it all back in, just clip it off.