Complete coverage of workbench effect radius is one of the only effective methods of eliminating spawns, including those from event invasions (campfire & ward also work). Complete enclosure of an area by walls does nothing to deter spawns. I thought I had my boar/wolf pen blanketed, until I found some deer parts inside. I had missed a very small area and the deer was spawning on top of my wall. I use workbenches liberally, and only place wards outside my entrances. As well as preventing spawn wards increase material structure strength, so a gate that a troll could bring down with one blow now takes him 3+ to bust up.

I have found the most effective method of protecting my base from damage due to an invasion raid event, it to beeline it outside, over the walls to the edge of the event radius (red circle on minimap). I have built killing pits there to engage the enemies to ensure my 100% survival every time.