Hello. I am hoping to install a fixed timber gazebo. I intend to use post anchors set in concrete, since there is no existing concrete slab and the area is subject to water after rain. I am wondering how to get the four post anchors level (i.e. in height respective to each other), given they will be around 3.5m and 4.5m apart? I can use string to layout the base but that's a long distance to try get all four level. Thanks for any pointers.