I have a 6 year old Lab and a 5 month old boxer. My Lab was a serious garden bed digger as a puppy, and young adult, so I do sympathise.
We live in Barbados, and our house doors are are always wide open to the garden, all day long, so our dogs come and go into the yard freely, and probably spend as much time outside as they do indoors, so it was impossible to police her.
We had some success by providing her with a sandpit, like you have for kids, so that if we caught her in the act, when she was told no, she could also be shown an alternative that she was allowed to dig in. We would also bury chew sticks, and the like for her to find to make the sand more appealing than the soil. I also used to keep her with me whenever I was gardening/ planting and train her to "Leave it " if she showed an interest in nosing or pawing the plants and soil I was working with ..... I wanted her to consider the garden beds my property, much like you would teach to leave your shoes alone !
All this didn't completely stop the garden bed digging, I have to say, but there was a significant improvement, to the point that it was not a big deal for us. I just accepted that once in a while I may need to replant something, but it wasn't often. Of course it could just be that as she got older she wasn't quite as obsessed with digging . Nowadays she still digs very occasionally, but only ever the same two spots, which are under large shrubs and do no harm, so I let her do it .... not that I think I could stop her ! .... but the flower beds are safe
Now my 5 1/2 month old boxer - Oh dear, when she was between 10 and 14 weeks old, how she LOVED to chew on roots, branches, bite at leaves and pull them off, tug at plants to try to uproot them. Of course, at that age she was constantly supervised when outside, so we could intervene before too much damage was done. Thankfully she did outgrow her fascination with all things green, and hasn't attacked a shrub in weeks and weeks.
Hope your little one does likewise.
Jinny