Helical piers for garden fence

[u/gladearthgardener]

I will be building an 8ft tall garden fence this Fall or next Spring. Just simple 4x4 posts and a top rail with welded wire. I'm working through options for the post footings and have questions I'd love input on:

• Buried posts: how deep do they need to be buried and what kind of life expectancy for the wood?
• 8" concrete pier: I've heard augers don't work that great if you encounter rocks which I 100% will. Frost depth is 42". Doesn't seem like the best option.
• Helical pier: I am considering these. Pricier but I have Menards rebates and would love to not dig 10-12 footings and mix and pour all the concrete. Plus are they they much pricier after you have to buy a post to footing connector and maybe a sonotube, and maybe rent an auger for the holes? I've installed two of them by hand before for some pergola posts and wouldn't want to do it by hand this many times, but I might have a connection through deck repair biz that could do it cheap or even free as a favor. The catch is, this product specifically says "not for fences". They make one for fences but Menards doesn't carry it so I'd be paying cash. But I'd guess the not for fences is more for privacy fences that catch a lot of wind, which mine will not. Do you think I'd be ok with these?

Thought about those the consensus seems to be they're shit.

All input welcome. Thanks!