Our pens we built are 22 years old, the rest of the corrals (getting rough now) are 35.. all made from douglas fir.. one of the hardest 'softwoods' I know... House was built in 1936 and the nailgun will turn nails into noodles if you try nailing it.. especially where there's a knot.. Perhaps a Hilti gun would work there. I predrilled and screwed most everything I had to mess with while renovating