I want to build a 50x100 ft area to divide into breeder runs and a large "free range" area that will be use on alternate days. How long would the timbers last? 4x4x8's and 7 1/2ft T-post are $6.00 ea. and the timbers are 8ft. and will only run approx. $3.00 ea. so a huge cost savings but if they wont last then....