I love how the tips section clearly distinguishes that "pro" = "because of" and "por" = "for", but then they go straight into this, where it could go either way, but the better translation would put "pro" with "for".
It confused me too, until I thought of an alternate way to think of that sense of "for" (ie ="por"): use "meant for" or "dedicated to" instead of "for". If it works with the sentence, then the correct word is por, if it doesnt, and "because of" does work, then its pro. Have not tested this on other sentences yet, let me know if I'm wrong.
At least for the German speakers, the difference can be easily distinguished because there is a similar concept for that : pro <-> wegen, por <-> für.