Moving baldies around is easy. You either let them wander at will, and they will wander everywhere , or you can pick them up one at a time and drop them anywhere you like, even across water, so being on an island is no big defence. You can also, with enough red power, use angel wings to fly whole flocks of baldies to another place, or one of your own buildings, or an enemy building. Thing is, if it rains your flyers will crash, and if they crash over water they drown. If you don't go after the enemy baldies, they'll certainly come after you.
Attack is the best form of defence.
An invention can be placed anywhere on the map, as long as you have a free scientist outdoors to fly over and deliver it. Areas of water are no defence against that. Alternatively you can use your soldiers to attack with. Soldiers tend to go wherever you place your portable shield - put it near an enemy building and your soldiers will make their way over there from nearby areas. The intervening water really makes little difference, and thus the variety of maps is not that important.