As some might remember - I have written about it several times - I have changed one of Walters features - TheChineseCanal - to a useful canal. Something where ships can sail from the open sea to smaller inland seas or lakes. And the other way around.
To do this I had to make a change in the CIV4ImprovementInfos.xlm for the value <bActsAsCity> and change the line from <bActsAsCity>0</bActsAsCity> to <bActsAsCity>1</bActsAsCity> (and the opposite for Forts since I didn't want to see ships dock in a fort on a hilltop - it doesn't look so good in my opinion).
Unfortunately the AI changed its bad habit of using a fort to claim a bonus outside the city-radius to use a canal instead. And when I thought that a system of canals used in the way Walther intended - to irrigate fields - looked ugly, then..... this was even worse. A canal placed on top of a bonus in a place where it looked completely out of place (which it also was). Funnily enough, the AI is able to figure out how to use the right Improvement on a hilltop - but not on a flat tile. So this was something that I had to find an emergency solution for - the easiest thing I quickly found out was to place all bonuses on a hilltop. That's how it turned out, which you can see below on the next screenshot.
At the same time I changed Forts to what those should be used for. Forts - strongholds in the wild, along the borders or as lookouts. Manned with landunits only - not used as harbors or airfields.....
Now remember, that I play with a 5-tile distance between cities. Moreover, the country is in many places very dry (desert) or quite cold (tundra and ice), so there are plenty of inhospitable places. Places that only barbarians care about. So sure - forts are needed. Or at least as I have done here since I do not yet have access to Forts - I have placed a "strong" unit and a scout with the ForvardObservers promotion on a hilltop with a forest.
P.s.: In this game I'm going to test if I actually have found another - better - solution on the bonus_on_hilltop_only problem, which actually isn't a very good solution. I have moved Canals from Tech_Civil_Engineering (Classical Era) to Tech_Mechanical_Engineering (Renaissance Era). At that time, most cities should have been founded and only a few bonus outside city-radius unclaimed. It might be "visual acceptable" for me - time will show.