Sushi rolls opening up

I always dip my sushi in a little bit of soy sauce/rice vinegar mix - or, depending on the sushi, a bit of sesame oil and salt - but I had the same problem as you where the rolls were opening up.

I started making a smaller amount of whatever my chosen dipping sauce was and putting a thin film of it on the edge of the nori where they connected (think like rolling a cigarette - you're making a kind of gummed edge). This works great, and I've replaced the sauce entirely with just this sticky-mix. I'm still getting the flavor but not eating as much sodium via the soy sauce and my rolls are staying together nicely.

If you don't want to do it with sauce, you could use a bit of water in similar fashion and I think that would work equally well.

The two most common causes of rolls falling apart are they are either overstuffed (too much filling) or the nori is too dry. dax's answer will work if the nori was a bit dry.

My memory of watching Japanese cooks make sushi rolls is that they use a bit of the rice mashed against the seaweed sheet to stick it together. Like glue.

Mashing the rice works as well as dampening the edge of the nori. Try the inside out method Steve described using whatever filling you want. They are visually appealing and seem to hold together better. You can add toasted sesame seeds or caviar to the rice before flipping.

Leave room on the edge & don’t over-stuff it. Mix a bit of rice wine vinegar with tamari sauce. I prefer Tamari sauce over regular soy sauce, it just tastes better. Take your finger and put a little of the sauce on the edge of the nori roll (that you left) to roll it up.