Something that can happen without you even noticing is your stoma will drip fluid down your abdomen. It's hard to see because it happens right below your stoma, so getting a good visual without a mirror would be next to impossible. 

This is why I tend to wrap my stoma up in gauze while I'm preparing my wafer during an appliance change. If you don't do this, then double-check that your skin is dry under your stoma by wiping it before applying your new wafer.

Hopefully, this will help people who've had leaks, because one little drop running down your skin is enough to cause your wafer to fail.