I think the solution would be to request to modify NDA to be very specific to exact project (include project name + exact precise description + server stack + a

I think the solution would be to request to modify NDA to be very specific to exact project (include project name + exact precise description + server stack + anything, etc. - as as whole), so that it would be literally impossible to violate NDA working on a very similar project with minor differences. If potential client will continue insisting on vague language - scrap him.