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Can someone please explains these metaphors with one example of each?

A ghost from the past

The sea has no fences
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Actually, guest1010, some people believe that a ghost can really hunt you! You can describe some terrible events happening to you caused or done by a ghost from the past, since you have treated them badly when they were alive, or the ghost is an evil one and hurts anyone on his way.
This is only my own opinion. Others will certainly show up to help you out.
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Well, to me a ghost can only be from the past. Something, a thought you can't get rid of and that haunts you day and night.
I wouldn't call this a metaphor.

As to "the sea has no fences", I find it a nice image.

Though, for both examples, I think we lack the other term of the comparison.

E.g. : " love is a fenceless sea", meaning there's no way you can refrain love from invading your thoughts, etc...