Contrary to popular belief, gnomes do not merely turn into statues when mortals see them. In the old days, gnomes were often nuisances, meddlers, and thieves, and while their antics never rose to the level of harm, their constant pesting needed to be answered.
Someone, no one is quite sure who started the tradition, came to have the bright idea to put a spell on the offending gnome, causing them to freeze into a statue-like state. From there, they could be placed into gardens and be both a warning to others, and to be quite cute décor. This became a bit of a fad through the years and is now so prevalent even mortals can pull off the spell. It has even become a common punishment among gnome society.
Now, there is a caveat that must be considered. The spell operates on a fairness rule; the gnome was caught in the act of mischief-making, to which this is an appropriate punishment. Though, they may disagree; they are now a statue, and have little say in the affair.
Still, ensorcelling a gnome in this manner obligates the ensorcellor to care for them. That means, keep them clean, repair any chips and cracks, and repaint as necessary. Failure to do so will cause the spell to break, the gnome to flee, and the garden to wilt.
Many even take the time to have daily conversations with their gnomes to keep their minds engaged and spirits jolly. And there is advantage to this; the presence of a gnome helps the cultivation of flowers, the suppression of weeds, and the bringing of luck, all of which come about more readily when the gnome is well cared for.
I myself have my own gnome, though she does hold the odd distinction to having been a human before being turned into a gnome. However, I find this to be irrelevant, as she was caught in a game of gnome theft and relocation. Thankfully, all the misplaced fellows were merely statues, none were harmed, and all have been restored. This, I think, qualifies as the appropriate mischief-making for the use of the spell.
And the proof is readily seen: she now lives in my garden and has brought it great benefit for some months now.
Addendum: It has been brought to my attention by the gnome Grumpkin that he was the offending party in this plot, that he felt bad about framing the young woman, and wished to take her place. I thought this very magnanimous, thanked him for telling me, and sent him on his way. I am quite attached to my current gnome, and whatever unknown mischief she engaged in is enough for this to be an appropriate, fair, and just punishment.
Thus, she will remain an adorable, and well cared for, addition to my garden for some time to come.