Building massive seawall around endangered Islands like Mauritius to save from climate change Would it be possible to build a massive seawall, say maybe even made from metal that could rise as the sea level rises to prevent being erased? 

I am not considering costs here, nor beauty, only if such a wall would be able to resist the force of the entire ocean trying to get into the "empty" pool. 


Is it feasible?
What kind of material would be required? How high could one go? 
In the event of a leak, "terrorist" assault, what kind of disasters and how quickly would the Island become "erased"


You can give an example approximation on the size of the Island. 

Just theoretical.
This is more of an engineering question. For some situations it may be possible to build such a wall around some islands. Such a sea wall would be a cofferdam, which have been used for small scale temporary projects.

Complicating factors would be:


The height of the sea wall and how much water would need to be held back. 
The depth of to the sea floor. If the island is the tip of a seamount with steep sides and a large depth to the sea floor then a sea wall would be impossible.
The depth into the sea bed that the wall would need to be anchored into, or the wall would need to sink into, for the wall to be stable.
The wall would have to be able to withstand typhoons/cyclones/hurricanes,  small tsunamis and seismic events.


A metal wall would not be a long term solution due to corrosion of the metal. The most suitable material would be rock or concrete. Such a wall would need to be very wide. However, over time, even such a wall would need to be replaced/repaired due to sea erosion and battering.

Securing the wall against leaks would be critical and such a system may require solar power pumps to continuously move excess water out of the enclosure.