The 20-year old midfielder was being heavily linked with a summer move to Nottingham Forest but remained at Tynecastle after the summer deadline closed which delighted Locke.
However, the Jambos boss is well aware that it will be difficult for the Edinburgh club to hold onto Holt forever.
"Thank God he's staying, it's massive for us. We can't afford to lose any more players," he told Daily Record.
"Jason knows the situation. He came in and spoke to us with his agent.
"It needs to be an acceptable offer, that's the thing. We aren't just going to let all our players leave here. If they are going to leave, then it will have to be for the right price.
"I imagine Jason will attract more interest. That's great for him and for the club. But at this stage of his development, he's better playing first team football."