If you are going to pour concrete footings for fence posts or glass balustrades, there are a couple of ways to go about it. Obviously, you want your post to be as deep as possible so it can be strong, but that doesn't necessarily mean you'll be able to dig the hole as deep as you would like. That is, the more post you have underground, the stronger the overground post will end up being, but it's not always possible to dig that deep into your soil. This is why concrete footings are so helpful.
First, you need to dig your hole. The depth of your hole really depends on several factors. Most importantly, it depends on how tall your posts are going to be. It is a good idea if your holes are at least half as deep as your fence is tall. So, or a 6' tall post, you would want 3' of post underneath the ground.
But, if you are having trouble digging 3' deep into your soil because it is too dense, wet, or rocky, you might just want to dig a wider hole and pour a bigger footing. If you are able to dig your hole a full 3' deep, then you should try and dig it as narrow as possible. But, if you can only take 2' deep, for example, you should just make the whole a little bit wider. If your hall is about twice the diameter of your fence post, it should be plenty strong.
Mix the Concrete in the Hole
Another trick for creating strong concrete footings is to mix the concrete and water together in the hole. Don't mix them together beforehand and then pour the concrete into the hole. You can just pour half of the water and concrete into the hole and then set the post in it. Then, pour the rest of the concrete and water in the hole and begin to mix them all together. The concrete should start to harden very quickly, so you need to make sure that your posts are stable and level. That is, as the concrete dries, you won't don't want them to shift or tilt. Most people just prop up their post with a piece of wood. You can use pretty much anything that will hold your post in place as it dries.
It is not difficult to set fence posts, but it is vital to the eventual strength of your whole fence.