Looking for a solution to install lamp posts in the soil without screwing them

Hi. We have designed a 'base' for lamp posts that can be used outdoors such as in homes, gardens, parks, etc. Attached is the image of the same. But the issue is that we can only install it against solid floors such as on concrete or interlock tiles etc where we can drill and bolt it on the floor. But when it comes to sand/soil we are unable to use this 'base' because we can't screw it against the floor. It's true that we can dig a hole of 3-5 feet and put the base inside and cover it with sand but not sure how it can withstand the wind. The lamp is supposed to max 5KG weight and the max height of installation is 10-12 feet. So we are looking for a solution where it can be installed on sand/soil. It could be an extra accessory or a change in the current design of the 'base' plate or anything. Feel free to ask questions.