Maybe 12 times/year on average?
I don't really try to avoid it, but there is just no need. When the tank was new I felt the urge to rearrange stuff all the time. Now the tank pretty much just cruises on autopilot and I'm happy with it.
The most common reason for putting my hands in the tank is when taking out the wetside of my Vortech MP40 pumps for cleaning. I must admit I do this WAY to seldom. Right now you cannot see a single algae-hair in the tank, except inside the vortechs; they are FULL of hair algae

I guess I clean them every 2-3 months or so? When I do, I always make sure the air-inlet to the skimmer pump is clean as well. I have fully cleaned the skimmer pump maybe two-three times in 4 years? (All were probably the first year. lol)
My Vortech return pump has not been serviced/cleaned a single time since I bought it almost 4 years ago.
I very rarely buy coral, as shipping is anywhere between 50-100 USD :| When I do, I always glue them, so they stay in place. Id say max 2 times/year.
If there is something I want to remove (like an empty snail shell or a small broken sps branch (stupid fragile montis) on the sandbed, I just use the algae scraper and push it over to the back wall and lift it out that way. (back wall is black, so no worries if it should scratch slightly.