How to install fencing upright?

[parapaul]

I'm fencing part of the garden sometime soon. I've got all the necessary wooden posts and panels, and planning to erect the blasted thing something like this:

Dig hole
Layer of hardcore for drainage
Post in
Dry mix around base of post
Leave to set
Then fix the panels once the concrete has set

Now, I'm fairly happy to get the horizontal level right, but I'm flummoxed about how to get the posts vertical in two planes. Does each one have to be propped from 2 sides until the concrete has set? Do I just have to live with a garden that resembles a wooden meccano set for a week?

[parapaul]

Thanks for the replies

Postcrete - is that a purpose-specific mix that sets quickly?