This may sound a bit odd but take a lesson from old people. Their balance isn't the same as when they were younger so they use a cane as a third leg. When we wade in moving water (or on slippery rocks), maintaining balance is just as challenging as that old person. We all have a canoe or kayak paddle that is very strong. These paddles make an excellent cane. Their reasonably flat edge can be temporarily lodged in front of small rocks under water providing a very stable brace. This certainly beats trying to cross the stream with just your feet. If a foot becomes accidentally stuck, shifting your weight to the paddle and backing out of the crevice will normally dislodge the foot. Here is a video by Fergus Coffey (Zoar Outdoors) that demonstrates this technique: Solo Wading Technique.