Sorry I got in late on this one.
I understand that Paull H. may not still be checking in on this but I am one that has built all of my ma weapons and equipment so I will give a brief explination of my makiwara board.
Mine is mounted in the concrete floor. It used to be outside but the dirt kept giving way and loosening at the bottom, plus I was a bit imbarrased when the neighbors would ask what that pounding sound was so I took it inside.

It only cost me about $5.00. Actually is was just a scrap from the deck I built on my house. The wood I used is called iron wood or ipe. This stuff is great. It is atleast twice as heavy and strong as typical deck woods. Guaranteed to last 50 years on a deck even over water.
This ipe wood came in 3/4" x 5 & 1/2" width. At first I just planted in in the ground and tied 2 layers of leather at the top 10" but it was so heavy it shocked my body all through my arm and spine. I used a belt sander to taper it down to a little under 5/8" at the top and that took care of it.
Still...if I do not use it for a period of time it is a bit tough on me but soon enough I am back up to 500 plus strikes each workout.

Hope you get what you want out of your makiwara board. It is a great training tool.