Topping the front yard wall

To get the top of the front yard wall straight, we have run a string from one end to the other.  The top of the cement wall is about 10 inches below the string.  We experimented with 6x4 and 8x4 limestone blocks to put on top of the wall, and think the 8x4 will be better.

I tried to lay stones on the top of the cement wall, but I don't think I have enough skill to do this the entire way.

So I should probably hire someone to do a good job.

But I can go ahead and buy the rock and have it ready.  8x4 limestone blocks.  620 pounds for a total cost of $42.89.

That is not quite enough, but it is as much as I could get in the car.  I need another 10 feet or so, but I also need to finish the wall to the street before getting this done.