I have a negative edge in the deep end of my pool that is about 15 feet wide with about 1 foot of tile on top of the wall over which the water spills into a catch basin. I had the same question about cleaning robots and had a hard time finding a definitive answer. I just purchased a Dolphin Nautilus Plus robot and used it for the first time last weekend after opening the pool. I watched the robot climb the negative edge wall several times. About one quarter of the robot body went above the top of the wall, then it sensed air being sucked into the robot and it stopped climbing. Once the robot senses air, it will stop climbing (for this reason, the robot doesn't clean the top of the stairs). In some cases, it stopped and turned sideways, going across the side of the negative edge wall near the top. Other times, it stopped and then backed down the side of the wall. At no time did it seem like it risked tipping over the edge, since the robot always stopped long before enough weight of the robot would be above the wall that could cause it to tip over the negative edge. The robot ended up running for about 2 hours the first time I used it, with no issues at all. In fact, the pool has never looked so clean!!! So far so good, and I would definitely recommend the Dolphin Nautilus Plus assuming it continues cleaning like it has the first time.