The phrase "a difficult obstacle" is correct and usable in written English.
It can be used when describing a challenge or barrier that is hard to overcome.
Example: "The team faced a difficult obstacle in their quest to complete the project on time."
Alternatives: "a tough challenge" or "a significant hurdle".
The right-back is a difficult obstacle to get round.
Manchester United in 1981 were not the latter day Manchester United of Alex Ferguson but Dave Sexton's team still presented a difficult obstacle.
Fire performance is often identified as a difficult obstacle to overcome in designing lightweight sandwich panels suitable for use in building applications.
England will have to cope with enormous expectation and even their first game against Fiji is a difficult obstacle but the power of their pack, in particular the tight five, will make them hard to beat at Twickenham.
"The western perceptions of China as an ageless rural country with a repressive 'red' regime remain a difficult obstacle for Chinese filmmakers – other than by designing these fantastic tales of martial arts set in ancient China," says Yingjin Zhang, author of A Companion to Chinese Cinema.
In searching for these "Hawking points", cosmologists face a difficult obstacle as the CMB is faint and varies randomly.
But nothing poses a more difficult obstacle than what is disguised on the menu as ma-la fried tofu.
Low humidity makes the egg shell a more difficult obstacle for larvae to chew their way out.
A more difficult obstacle faced by Black Canyon, said Steven Stern, the co-senior producer, was the refusal of Barbara Lewis, one of Chamberlain's sisters, to cooperate.
It's an incredibly difficult obstacle for younger workers in their first job to overcome.
In the show – the first Australian spin-off of the long-running Japanese show Sasuke – competitors attempt an increasingly difficult obstacle course, most of which is held over pools of water.
