Our dog has selective hearing to training. He knows he's not allowed in the beds & will come out (at high speed, damaging everything!) if I really sound like I mean it.
He wanders through them whenever he thinks I'm not watching though.
I tend not to use bonemeal, let alone blood, fish & bone as he dug up all the roses & bulbs when he was younger until I realised it was the smell of the fertiliser that was attracting him!
Training to use a specific area might be worth a try. Ours loathes water being squirted at him, but will put up with it to do whatever naughtiness he wants to usually, or just return to it later. Some dogs are very determined!