Q: How I can protect my tables ( .dbf files ) against to open with any other Program (like Excel, access) ?

A: There is too many method to solve this problem. Sadly non of its has warranty, always there is a solution to open any file by experienced users. You can ask Google.

Against non experienced users one method will be changing file extensions ( .dbf ). In this case you need modify your programs to change “file name” ( open dbf ) parameter  in USE statements (USE commands or DBUSEAREA() functions).