The above photos shows Larch Tongued & Grooved Board Wall Top Fencing. This timber can be left to weather naturally but is also the ideal choice if you wish to stain or paint as it will give a beautiful finish. Also available in Oak and Iroko hardwoods. 

Tongued & Grooved Board Fencing is a strong, smart and solid fence. The design compliments many of our solid gates and so it is a great go to solution for a wall top side panel as shown here. But works equally as well as an entire fence.
As with most wall top fencing it is fixed to independent full height posts behind the wall it adds no strain to the existing wall structure making it perfect for older walls.
Constructed on site it is available to any height , shape and formation.