The phrase "a layer of defence" is correct and usable in written English.
It can be used when discussing security measures or strategies that provide protection against threats or risks.
Example: "Implementing a layer of defence is crucial to safeguarding our network from cyber attacks."
Alternatives: "a level of protection" or "a barrier of security".
There are plans to run a pilot programme with sex workers in Kenya to see if it could be practical for them to use PrEP as an extra layer of defence.
And why the strongest military power in the region needs another layer of defence via an international force, to secure it from the weakest and least powerful party in the area, is simply beyond argument or reason.
Now scientists realise that there is another layer of defence inside the cells where it might be possible to enhance the natural anti-virus machinery of the body.
But then Mum removes his thick bifocal glasses to adjust his breathing mask and suddenly, with that last layer of defence stripped away, he looks every day of his 82 years.
Epithelial barriers provide the first layer of defence by limiting the access of potential pathogens.
As another layer of defence, plants have developed the ability to recognize such microbial effectors by additional receptors (resistance proteins, R) to activate the effector-triggered immunity (ETI).
Another layer of defence is provided by resistance (R) proteins that detect these effector proteins initiating effector-triggered immunity (ETI), a type of resistance typified by the hypersensitive response (HR) associated with host cell death [ 22].
Subsequently, certain plants recognize particular effectors, or their activity, by resistance (R) proteins, which lead to activation of the second layer of defence, effector-triggered immunity (ETI) [ 16, 17].
Now comes the layering -- first a layer of sweet, sticky rice, then a layer of mango.
