Hi mate, thanks again for all your suggestions and feedback!
People on boats and walls will fallback to a low level mode, which will increase the performance. This mode allows to place many ranged units on walls without cpu impact.
I will check the harpoon bug. Sharks are useless at the moment, they are decorative units, but maybe I will add what you suggested for them.
Ballistas, mortars and animals can't be placed on walls at the moment, because the movement of those kind of units is limited.
I could add height aim to the ballista, so that you can add it on walls. The bugs with ocean battles will be fixed asap.
The next update won't take as much time as the last one and I'm thinking about adding more smaller updates instead of working a month or more on each update...