The terrorists will go for the easiest target that gives the highest "reward". Secure one venue (theme park/ visitor attraction/ stadium/ airport/ shopping centre/ etc.) and they will choose another.
On the world stage I think that Madam Tussaud's and the London Eye are Merlin's two most prestigious/vulnerable attractions.
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Security at AT is more important for preventing anti-social behaviour, vandalism and theft than for preventing a terrorist incident. If a gunman (gunperson?) got into the park there would be little that a few unarmed security guards could do other than evacuate areas and wait for armed police to arrive.
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From the Disneyworld perspective the Orlando shootings has taken news coverage away from their parks
natural hazards