"unrelenting control" is correct and usable in written English.
You can use this to describe a situation or person who is extremely strict and does not allow any leniency or flexibility. For example: "The manager at my job has an unrelenting control over the workers, making sure that everyone follows his rules exactly."
Canada is a wildly impressive novel that demonstrates what John Banville, reviewing it for this newspaper, called Ford's "unrelenting control" over his prose.
Drafts of her love letters have survived: they are witty, confident, open (not coded like letters to "Master"), and within the limits of her unrelenting control over her existence, abandoned – hardly the way 19th-century ladies were supposed to behave.
Watching Tumi own the stage in Lilongwe this year I remembered what it was that makes this guy one of the most consummate performers South African hip-hop has: flawless timing, unrelenting breath control, commanding presence and a warm magnetic charm wrapped around his complexly layered lyrics.
The observed high re-infection rates call for unrelenting malaria control efforts, which should not ignore the asymptomatic sub-population, if malaria is to be ultimately eliminated in this area.
She was followed by a young man who sang a song he called "Eclipse," about unrelenting stars that control destiny.
Neither have her crusading for gay marriage, unrelenting demand for tough gun control, nor her warnings of putting coal miners out of work.
Somalis also described to Human Rights Watch unrelenting daily repression and brutality in areas under al-Shabaab control.
And once Republicans took control of Congress, they subjected the Clinton administration to unrelenting harassment — at one point taking 140 hours of sworn testimony over accusations that the White House had misused its Christmas card list.
And many ordinary Palestinians, especially those who still live under Israeli security control, assume that any lull in what they see as unrelenting hostility against them will be short-lived.
His tenure was marked by unrelenting criticism of US gun laws and his ardent campaigning in favour of gun control, leading to high-profile clashes with opponents and a nationwide petition calling for him to be deported.
