Occasionally, there are lapses in the structure of said liners, (for instance when seagulls peck at the edges), and the massive outpouring of water can lead to catastrophic consequences, such as the recent Asian Tsunami.
The original asbestos liners first installed in 1805 are gradually being phased out and replaced by the more reliable rubber kind. These are probably less likely to violently explode on contact with water - a flaw which is probably the main reason why the current liners get such a bad press. The work is expected to be completed in late 2050, when the government is confident the world's oceans will have evaporated enough for the Marianas trench to finally get its lining. At this point, we can apparently look forward to the first ocean water-features being installed, or alternatively a novelty birdbath.