Even then they'd still try, IMO its one of their best traits. My old jag (~7") would dig out a pit about a foot in diameter between two large rocks, and right down to the glass with about 3" of gravel, piling it up to around 6-8" high in front. Every week I'd fill it in doing a gravel siphon, and he'd have a bit of a go at the siphon in protest, and as soon as I'd finished he would be digging it out again. I found he wasn't too aggressive other than when something else came near his pit, but I suppose at 7" he was only half grown.
I might even have a pic somewhere...