Dear Er Qadri
I would imagine that you are involving the students right at the stage of proto-type development and not just after you have developed the prototypes. If so, you need to bind the student through appropeiate written agreement prior to start of the project implying he/she would maintain confidentiality and would not exhibit, present or publish the work or results of the project anywhere without your permission and that the IP rights emanating from the project would be assigned to you or to your department. You should yourself also excercise due restraint till a provisional patent is filed.
I am a technologist turned Patent Agent and also designated as 'Scientific Advisor' to the Patent Office. I shall be happy to advise you on the type of agreement you could enter with your students and also help filing your patent applications, if you would want so. Please get in touch with me at firstname.lastname@example.org or at 011-45630873 (O), 011-25446234(R) and 9810096099(M).
Dr Rajendra Prasad, Founder: Technology-Patent.com.