SIXSwordS, you’ve got nothing to worry about – this is a very small deal with practically nothing riding on it.
Not contacting a current employer is very much the standard. Indicating that you don’t wish for your current employer to be contacted will not take you out of the running for a position, nor will it even raise an eyebrow. It will be understood by 99.99% of employers. It’s not something you have to tiptoe around.
The only reason employers even ask this question is because it sets their starting-off point in researching your employment history. No one’s out there saying “yeah … Person A is a lot more qualified, but Person B said we could call his current employer! Person B therefore gets the gig!”
Alternatively, you could indicate “no”, with the reason being “This resume is submitted in confidence”. That will more than suffice.