The phrase "a hard time retaining" is correct and usable in written English.
It can be used when discussing difficulties in remembering or keeping information in mind.
Example: "Many students have a hard time retaining complex information during exams."
Alternatives: "struggling to remember" or "difficulty in keeping".
Law enforcement agencies here are having a hard time retaining recruits, who soon discover they can make a lot more working in the field.
On June 17, however, Coldplay will release its fourth album, "Viva la Vida or Death and All His Friends" (Capitol), and even Mr. Martin is having a hard time retaining his modesty about it.
And even when they do, they have a hard time retaining them.
If there is just one path to success in your firm, you will have a hard time retaining a diverse group of talented employees.
Much like Uber or Airbnb, it's an idea that could branch out to any city in the world where retailers have a hard time retaining qualified staff.
There are a lot of reasons why people have a hard time getting into the workforce or have a hard time retaining a job maybe because they haven't built up the skills or they haven't built up the behavior patterns needed.
At the same time, he says bigger classes can frustrate teachers, making it hard to attract and retain talented ones.
So did they find it hard to source food and retain a clientele?
You'll find school districts that receive fewer property tax dollars and schools that have a harder time retaining and paying good teachers.
European countries, however, have a harder time retaining foreign students after they graduate than "destination" countries like Australia, Canada and the United States, in part because the path to citizenship is seen as easier there and opportunities for social mobility are greater.
They'll have a tough time retaining the middle.
