What are you trying to protect your trees from, rabbits, deer, or something else? Probably rabbits since you are talking about those plastic tree guards, but deer are my problem. If I don't protect my young trees from deer, they will keep them nibbled down to where they cannot grow and will kill them. I also had a buck that rubbed the velvet off its antlers on my young tree trunks, killing two apple trees and a hawthorne and injuring several others.
I split a treated 2X4 lengthwise, then cut that in half on a diagonal to make a point. I drive three of these around the tree about 2 feet from the tree and put 5 foot long wire around that. I use 3/4" poultry staples to attach the wire except for that last closure. I tie that with something I can undo so I can get to the tree to mulch or pull grass, string if I use plastic fencing or wire if I use wire fencing. On the blueberries I use a snap lock to close it so it is easier to get into often when those blueberries ripen. If you use heavy enough wire, you will only need one or two posts instead of three but weigh the cost of the heavier wire against the cost of an extra post and the extra labor to put the post in. If you don't like treated wood, you can use those metal posts. Cost was a factor for me.
In the area where I have my fruit trees, the ground is too rocky to drive the sharpened "post" into so I use post hole diggers and set the treated 2x4s. I rip these in half but leave them 8 feet long. I set them about 3 feet from the tree and use two strips of wire or netting 3" wide to get a little more coverage. I've tried plastic netting and chicken wire on these. They both work and the sharp edges of the chicken wire will get you when you are pulling grass or mulching, but chicken wire is a lot more durable than plastic netting.
Deer can easily jump a 5' or 6' fence, but if you keep the landing area small enough, they will not jump into it.
This will not stop deer from nibbling any branches that grow out of the fence and they can still get to several of the branches or much of the fruit higher than the fence, but it does stop the deer from killing the tree. If you choose your wire right and watch how you attach it at ground level, this will also protect against rabbits.
There are many different ways to do about anything. Just mentioning what I do so maybe you are someone else can adjust it for their use.
Good luck!
