'a firm link' is correct and usable in written English
You can use it to describe a stable connection between two things, people, or ideas. For example, "The new partnership between the two companies created a firm link between their businesses."
A recent IMF staff paper found a firm link between the balance-sheet strength of Italian banks and their borrowing costs.
The group's attacks on the Kurdish leadership give it common cause with Saddam Hussein, though a firm link with the Iraqi dictator has not been established.
In the hands of Isaac Newton not only was the study of colours put on a rigorous basis but a firm link also was forged between the experimental science of mechanics and observational astronomy by virtue of his law of universal gravitation and his explanation of Kepler's laws of planetary motion.
Law enforcement and intelligence officials say that the police have not established a firm link between a round of bombings July 7, when the 4 bombers and 52 other people were killed, and the botched attacks July 21, when no one was hurt.
It has been known since 1967 that a firm link exists between the fixed point theory for nonexpansive mappings and mapping theory for accretive mappings.
In doing so he made a firm link between international trade and international peace, believing it key to unlocking world economic potential.
Prosecutors had said that Dr. Aquino caused Parkway to make $60,000 in payments to a firm linked to Mr. Kruger.
Most of this is managed by a firm linked to Mr Kovalchuk.Companies linked to Mr Kovalchuk also control most television advertising.
South African media have reported that a senior anti-corruption official plans an investigation into the awarding of government contracts to a firm linked to him.
Since that race — where much of the television advertising was handled by a firm linked to a former party chairman — the committee has broadly expanded its roster of campaign and advertising consultants, bringing in highly regarded talent from the Beltway.
The registered owner of the land crossed by the path - which was blocked by a barn, a gate, barbed wire, and refrigerators - was Rarebargain, a firm linked to van Hoogstraten, now serving a prison sentence for manslaughter.
