Striker John Akinde turned down a loan move earlier this season while Sergio Torres also admitted he could have gone out on loan last month but is determined to force his way back into Barker's plans.
And the Reds boss believes it can only be a good thing having such fierce competition for places.
"It is their careers," Barker told Crawley News. "When someone comes in for someone I let the player know there is interest and leave it down to them on what they want to do.
"But sometimes that is not the case and some want to stay for football reasons.
"I hope I create a learning environment here and that people want to stay for the right reasons.
"We have had some turn things down and I see that as a positive that they want to be here and fight for their place."