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you need to have the base of the barrier supported by a build that is connected to the objective, so when the objective is destroyed, the barrier block is destroyed
bludrive did this with a supported a barrier. You can get fairly far with this type of solution.
More complex ideas are being planned :). We appreciate all the ideas in this post!
Also would love an option where if the opponents objective is broken they have no more spawns
Take a look at BluDrive’s featured map it has something like this.