The market tells us (IN FACT IT IS SCREAMING AT US) that anyone you hire will stay somewhere around 2-3 years (there will be exceptions, of course). Regardless of the years of seniority or level. If you are still fighting this, I urge you to reconsider your stance and to recognize why it isn’t a problem;
When you bring someone on board, you should be doing so with specific goals in mind. None of us know what is coming down the road, so why pretend we know what we need from the new hire long term? What you do know is what is needed now and the foreseeable future and this is where you need the new hire to be successful.
Hire resources on a “TOUR OF DUTY“. It is a win/win! This entails hiring someone as an employee of the company, taking on full responsibilities (P&L, resources, etc) but there are specific goals to be met, for example, developing a product, developing new business, selecting and implementing a new ERP, building a new department, and so on. These goals will define the TOUR. At the end of the tour, if there is another tour and both you and the candidate agree for more – go for it! And if not, you shake hands. They walk away with more experience and a successful story to bring to their next position and you have achieved your goals and can replace them (if you need to at all) with someone who meets the next set of goals.
To continue hiring with the awkward words nobody speaks upon signing an employment agreement, which are “this will be great until one of us doesn’t need the other any longer”, makes no practical sense. Be up front. You will have a better chance of retaining the employee for what you need them for versus having to worry about them leaving before the goals have been achieved. Pretty much everyone like to have a win, and the ones who don’t or who don’t care, are not the ones you want working for you. If you are upfront in defining the circumstances, the employee knows exactly what they are signing up for and what they will walk away with once they have completed the work. On the employer’s side, you will have better success in meeting your business objectives. Win/win. The end.