I try to stir up the back of my tanks with a stick in the tight spaces every once in a while. I try to arrange my tank so that it is cleanable. I thought that hydrogen sulfide buildup was really only a danger when sand that would compact, but my problem came with gravel. I also believe that my problem started to develop after trying to use a black grit (sandblast grit) as a substrate. Looked great, but was too sharp for my corys. when I changed that substrate, I really smelled the sulpher, but the fish were out of the tank. I did not capture all of it and think that the anerobic bacteria was still in the remaining substrate which spread to underneath a few ornaments. When I did a 'deep cleaning' I think I released it.
I have one tank with pool filter sand. It has a few places that are very difficult to mix up. I bought a dozen Malasysian Trumpet Snails (MTS). They burrow in the sand and help mix those hard to reach places. Still waiting to see how that works. (I was afraid of snails over-running my tank, but was told that if I saw my snail population going out of control it is probably due to overfeeding.
Hope this helps. Sorry if I rambled.