fencing on a slope

can anyone give me some advice on fencing my front garden, which is on a slight slope.l want to use 4 ft panels , so what length should the wooden posts be, how far in the ground should l put them,and most of all the method to step down on each panel. l need to put 5 6x4 panels up.

Use post long enough so that you will have 2ft in the ground, remember to take the fall of the slope into account.
Start at top of slope, put first post in deep enough so when panel is offered up 3 inches of post are above the panel. Remove a weather cap off of one of the panels (beveled cap on top of panel), this will give an exact 6ft length, butt against first post now dig hole at other end. Fit panel again leave 3 inches of post above panel. Dig next hole & fit panel but remember that this panel will be stepped down (keep the bottom of panel on the ground at the high side of slope).

For a fence on a slope I would allow each post to be 3 foot longer than the panel.
2 foot in the ground and a foot above the panels to allow for stepping.
Around here an 8' post is likely to be cheaper than 6' or 7' ones so could be cut to length after the fence is completed.

I erected 10 panels down a slope and to get the drop for each panel I used a spirit level on the top panel. At the last post position but one, my friend held a batten upright with another up it that he could adjust to my sight line on the top of the level. Holding the two together I measured the length of them.
I took one panel height from its length then divided the rest by 8. For me this gave about 4ins. drop per panel. I did it this way because I didn't have a bit of string to make a line between the posts to get the drops even. It worked out okay fortunately. But next time I'll use a string line.