4 X 4 Swing Sets Blueprints Should I Use Untreated Fir For 4 X 4 X 8' Posts For A Swingset? Contractors, Could You Answer This?

Should I use untreated fir for 4 x 4 x 8' posts for a swingset? Contractors, could you answer this? - 4 x 4 swing sets blueprints

My husband and I built a playground in a few weeks, 5 4x4x8 'Peices of wood requires. My father left untreated, some pine is good enough to give us, but I'm not sure that the tree was in this type of application. The wood of my stepfather was stored in the garage and only a few months.

Linking Swing
http://www.homedepot.com/webapp/wcs/stor ...

These amounts are 4x4 in the tower on the right side, and one of them will be support to the swing bar. To touch the ground. My concern about the longevity is that we live in an area of rain in the United States, and it will be in a shady area. I noticed moss growing on the floor, so I am concerned about the positions of decomposition. We hope that this momentum will last about 9-10 years?

If we do those positions? Is it possible to treat them to last?