Don't worry about gas pockets. I have tanks with substrates up to 10" deep, never stirred, and I don't have H2S production. You'll get CO2, but that doesn't hurt anything.
A little about the science behind H2S: sulfide gas is produced by sulfate-reducing bacteria. These bacteria feed largely on dead plant matter (especially cellulose, AKA fiber) and "breathe" sulfate (SO4--). In order for these bacteria to establish themselves, they have to have not only an anoxic substrate, but also lots of sulfate in the water. If you do regular water changes (and your source water does not have abnormally high sulfate levels) you will not have enough sulfate in the water for significant H2S production to occur.