Specifics here are not good. Something like this should work: I'd like it to be a long time. Or As long as we both feel I'm doing a good job.

alternate answer would be like I am not a job hopper. I have my spouse working in this location.I have the educational background and job experience to work and continue in this job position. If needed in future I am willing to undergo training. Ideally I would like to work and advance both in career and personal front..the benefits pacakage promises good living standards and family support..I am sure it would be mutually beneficial agreement and I look forward to working at your company as soon as possible.