opinions on this please

[suzywong]

"layer after layer of security and fencing that shrink slowly "

should it be shrinkS slowly as the subject of the verb shrink is a singer layer?

[suzywong]

singLe layer, not singer

easily done but then I don't get to hand this post to a sub team on the Independent on Sunday as the author of the sentence in question presumably did

[Tigerschick]

Don't know really but my instinct would be shrink as there are apparently two things shrinking (security and fencing).

[ChipButty]

IMO 'layer after layer' suggests the plural layers and therefore shrink is correct. However, I do think the sentence could perhaps be rewritten as it doesn't read well.