I've had similar issues... tree trunks, electrical poles, signposts...
Static detection works... most of the time... for foreground large objects... sometimes! I'm not saying it doesn't work - I just haven't figured it out - yet.
What I ended up doing is to mask out those areas. Works great.
You may think... But you won't get alerts in those areas!. Yes, that's correct. But you will still get motion/AI in the areas around it. And, if the masked out areas are small enough, it wont be an issue.
In your case...
First image of the pathway between the fence & building:
, mask out the small areas where the items are by the brick wall. Motion/AI will not be detected there. It should not impact detection of people as it is small and low to the floor. Even if a person slithered on the floor next to the wall (unlikely), they would have to climb over or push the items away causing motion/AI detection.
Second image of deck:
Zone out breaks in-line with motion, like streaks. This will break up the falsely detected objects, but still allow motion detection between the zoned-out areas.
For example... (I colored the masked areas red to be more noticeable)

- gascan.gif (136.44 KiB) Viewed 535 times

- shingles.gif (137.85 KiB) Viewed 535 times
Increasing the 'Object size' may also help.
Raising the conformed % will work. But, you will loose detection of lower confirmed %'s that
are valid, which can happen in certain circumstances.
Another thing to consider If an detected person moves to/from the foreground, they will appear very large. The alert may be canceled if the "Reset detector when/Object size exceeds' is too small. You may want to increase it to 95 or 100, or disable it.