Wood decks and stairs are susceptible to rot and water damage. Use lag bolts to raise deck posts and stair risers above footings to prevent water from seeping into the wood.
Use your impact driver to drive 2 12mm lag screws into the base of your wood project and leave about 20mm of space between the head of the screw and the wood. This space will keep the wood from soaking up water and also provide an easy way to fine-tune the level of the posts by screwing the lag screws in or out.
Another way to protect your wood from moisture is to wrap the ends with a self-adhering waterproof membrane. This provides another layer of protection for your wood which will make it last longer.
Before considering these tips, check that they adhere to your local building codes.
Add 10 years to the life of your deck [The Samurai Carpenter (YouTube)]