Post concrete will set in the rain to most people's surprise, it's not ideal but will not prevent the concrete from curing although it will normally prolong the process. If possible always try and time your installation on a dry day or rig up some shelter to protect it.

To know how much concrete posts are really depends. It can vary depending on the sectional sizes of the posts being offered. In addition the quality of the production process. An old saying can be adapted here "Not all posts are created equally". Looking out for the right balance between quality and price can be a challenge.

To install concrete fence posts on a slope in the best way will vary depending on whom you speak to. Builders will all adopt their own way of doing things and consider it the best. When i install a fence for a customer ill adopt the "Dead man post" technique. You start by installing a very end post at the required height. Ill then go to the far end and install a temporary wooden post. I can then rig up a string line from one end to the other and follow that all along the run.

To install gravel boards I will always start by making an assessment of the posts my client wants. Most will feature slots/channels to accept them. They will arrive at the standard panel width for ease of installation and fitment.