The phrase "a layer of challenges" is correct and usable in written English.
It can be used to describe a situation or context that involves multiple difficulties or obstacles that are stacked or compounded.
Example: "The project presented a layer of challenges that the team had to navigate carefully to ensure success."
Alternatives: "a series of obstacles" or "a set of difficulties."
That anti-establishment sentiment seems like it could have presented a layer of challenge in bringing across some of Snowden's early conservatism, such as a moment early on in the film when Snowden winces at a left-leaning girl he just kissed (Shailene Woodley as Snowden's real-life girlfriend Lindsay Mills) and tells her "you taste like liberal".
Second, imperfectly optimizing individuals create an additional layer of challenges for providing job training services through market-based mechanisms, a potentially efficient way to deliver such benefits for standard rational economic actors.
I'm sure the founders would like to take the site to the next level, make it a business and that will bring a whole new layer of challenges – but it looks good so far.
Scaling up from pilot plant to commercial-scale facility presents a whole new layer of challenges that may prove unsolvable.
In a preseason interview in Argentina, during his South American exhibition tour, Federer said one of his hopes was that the new wave of men's players would assert itself in 2013, providing a new layer of challenge at the talent-rich top of the men's game.
The results here potentially add a new layer of challenge to the evolution of cooperation, not only for cross-feeding, but potentially to other mutli-species systems.
Homelessness adds a layer of difficulty to the initial challenges posed by poverty.
Not every version of heroism involves grand gestures, and the quieter ones present another layer of challenges to writers, who then must write character-rich scenes that underscore the heroic elements of their real-life protagonists.
Which leaves us with the dilemma of how to update our wardrobes... Instead of abandoning our inner Athena, we've decided to rise to the challenge, remove a layer of woolly jumper, and accent our winter basics with some serious, don't-mess-with-me jewellery.
In such a construct the main challenge is to generate a layer of adipose tissue replacing the hypodermis.
