Any general guidance for what size auger to use for fences posts. For example, if I'm sinking 4" posts, what is an appropriate auger to rent? Looking for any "rules-of-thumb" so I'm not asking to rent every auger they have. Also, if I do purchase a power head, what recommendations for augers on hand (sizes) would you have? (keeping in mind I want to purchase 2-3, maybe). I imagine larger augers can make plantings alot easier too. Thanks in advance!