If you are a small faction or just solo, I would recommend going down to bedrock, mining out a large area and then create an obsidian box to keep all your gear/spawners inside. one the box is big enough you should water it and claim it.
Many factions won’t raid the smaller ones because the loot gained is not worth the effort of building a cannon. However once you get richer and become a potential target; claim an area (on the border is best because it is less walls), trench down to bedrock, gen in your obby box, then gen trays of netherack at build limit to show where your walls will be, then gen a mixture of cobble and sand walls in the gaps, after this water the hole top, and break the nether rack. You can also build horizontal rev layers at the top and bottom to keep it more secure.
I would also recommend breaking the base up into floors or boxes with water protection in between so raiders have to readjust their cannon to get everything.
Good luck!