Ducks need a very gradual slope on the ramp - the heavier breeds especially!! If it's low enough I think it's fine without side rails - but mine do step or fall off the side of the ramp, which is only maybe 4 inches or so at the highest section, so if high enough to cause a leg injury if they fell off, I personally would put a side rail. I think a ramp is way better than steps. Some sort of grippy material such as astro turf or outdoor carpet will help them as well. I like that you're thinking of this detail!