Thanks for all the replies and ideas. I am open to all suggestions on how to place these. And would like to thank everyone in advance Thanks. I can not take credit for this because I found it on youtube here is the site: https://www.youtube.com/watch?v=o51xIDwMGkg
I changed some of the ways that I made mine by using a solid block of wood 4"x6"x6" I also drilled middle hole all the way through with 7/8" bit and used a 4' pipe to hold bricks in the middle with a 1/2" pvc T glued to hold them on instead of the string he used. I also used small nails to make sure the pipes stayed in until I sink them then I don't think it will come apart. Now that I have had some suggestions on how many to sink together and thanks again. I am going to put 4 about 6' apart in one place that I caught my most crappie in 12' water out from a point and 3 about 6' apart in two different places one in 8" and the other in 19' water that I also have caught fish. This is a reservoir that doesn't have very much cover for fish. I am going to use my handheld gps to find spot that i drop these because I was told that they are hard to see on fish finders. If these work I am going to make more and if they need more than 3 and 4 in places I will add more. The deepest place in this reservoir is 30' with most of it 4' to 12'. As far as sanding all that pipe I think I will do that on my next ones when all the pipe are in 20' sections also this is thin wall 1/2" pvc pipe $2.72 @ piece and is not real slick like the thicker expensive sc40 pipe. Please let me know any more suggestions. And the one that wanted to know drill bit sizes 13/16" spade bit for tight fit and 7/8" spade bit for the center hole that I put all the way through to hold bricks as weight.