What advice, strategies, keys, or elements would you suggest for creating challenging puzzles that aren't (reasonably) computer soluble?
I'm a programmer, so I can appreciate the argument that writing code to solve a puzzle is as enjoyable as solving it directly; don't take this question as any slight against computational solving. But I want to write good puzzles that people enjoy struggling with for a day or two; problems that can be solved via program typically lack this, in my experience.
Sometimes, as in the case of this puzzle, the inclusion of computers seems to take some of the fun out of it (as well as overshadow manual answers that deserve recognition) but there's no hard-and-true way to differentiate computer-generated solutions from manual ones.
Now, normally I'd say that riddles (e.g. What am I?) are the go-to solution for this problem, but they can get old very quickly (as evidenced here, based on some of the discussion). Another is cryptograms, but those also feel a bit tired sometimes.
Do any veterans of the site have useful tips or advice in this area?