For those landings i also have a plan already.
I think I will build a large amount of vessels, if he is gonna be sending me a fleet with units to land, i will sink his fleet with units included.
If he does not send me a fleet, i might send some myself, or i might just move my fleet in his direction in order to divert his main force that should be conquering AI ground back home for defence and thus waste valuable time and maybe allow the AI to punish him back a little.
An empty but scary fleet might also be nice to draw his units when i am gonna attack him over land
I still need to decide if i think the lighthouse is worthy to hide my fleet in open sea (and prevent him from building it and doing so)
I can't find any forums with Civ multiplayer strategies, is there none anywhere?