Timber knee rail is often used around car parks and retail areas, where the purpose is simply to create boundary demarcation and discourage pedestrians from walking over flower beds etc.  

It uses 100mm x 100mm rails which are supported on a birds-mouth fixing on 140mm x 100mm posts, secured via 100mm wide metal strap which is secured to the post on either side.  All timber is pressure treated and heights available from 450mm to 600mm.