The #internet is full of fun locking #garden #hack ideas for all sorts of things but almost always, they use #toxic materials that you really don't want leaching into your #soil. Even common #plastics like water bottles or #polypropylene turn quite toxic when exposed to #sunlight for a while. For example, https://rosal.web.uah.es/pub/Aquatic%20toxicity%20of%20commercial%20polypropylene%20and%20associated%20chemicals.pdf