Replacing fence post with arris tenon joints

[curium]

HI

I have a fence post in a fetheredge fence with arris rails. The post has rotted just above ground and moves with the wind. It is effectively being supported by the two adjacent fend posts.

I have included a picture.

View media item 71829
I think I'll need some cutting device to cut the arris rails from the fence post so I can take down the 2 adjacent fence panels before removing the fence post and replacing it.

This approach would require 4 replacement arris rails to be fitted into the tenon joints present on the adjacent fence post although.

I don't have the tools to make a tenon joint in the replacement fence post I have purchased. What tools would I require to do this?

I see that I can use arris rail brackets to nail the arris rails to the fence posts

 

[kbdiy]

If you could get good access to the base of the post then you could just dig out and drop in a concrete spur and bolt it to the existing wooden post, rather than having to remake the adjacent sections.