Attack the invaders when they are a unit and a settler. Add the captured wrker to a city and pop rush a temple. Keep a few archers circling about.-make sure ur cities can withstand at least a 2 sword invasion- Let them come. Bordering ur isle with units is expensive and unneccessary-and too-if a weak civ has tried to settle u may get tech in a peace treaty. Or if u are to late to prevent a city from being built, just build cities around it - rush culture building- and it will eventually flip over to u- free city-, or Let the enemy city grow to a 2 pop town- attack and keep it-there is a risk of it flipping back to the owner here however it should be minimal if its a one isle continent- u build lots of culture in it..pop temple asap - library (cathedral if ur there instead of library if ur religious)
Damn , just read 5 city challenge thing in the post now, i regress
kill settlers take wrkers.