Sell-locker: This item prevents you from selling a tower that has been built on it. It can also be placed over resources. When a sell-blocker is placed over a Sell Refund platform, it makes the building of a tower cheaper.

Tower-locker: Allows you to build only towers that are imaged on it, and can also lock modifiers.

Pre-built towers/modifiers/miners: then they places over platforms higher the map price especially when researches are locked. Counts like bounty modifiers and reduces the prestige