To prevent anerobic gas build up you can go 2 routes but its better to do both.
1. Reach your hand into the sand and stir it up,making sure you hit bottom while doing it. You could also use one of those plastic back scratchers that look like a claw.
2. Get Malaysian Trumpet Snails, they naturally burrow through the sand airate it.
If you have plants you don't need to worry about moving them, the roots will use the waste as food before it can turn gaseous.
You should stir your sand every week or 2. Don't forget to do under ornaments and caves also.
You can have a depth of any level if you follow these rules.
But if you don't feel like doing this I'd keep it under a half inch, but forget plants with a low level like that.