Barkoe
Economists call a market liquid when things change hands easily. A job market has become liquid when the people you would like to hire, and the people you would like to keep, can move between employers, contracts and countries with little friction. Most planning assumes the opposite.
You cannot slow the tide. You can decide ahead of time what you will do at each level of it, and that starts with sorting.
Three buckets
Keep
These are the people whose knowledge is hard to replace and whose next five years matter to you. Plan for them the way you would plan for a partner: room to grow, a say in direction, and a written answer to what happens to this work if they leave.
Season
Some roles are best filled for a fixed period, such as a product launch, a migration or a busy quarter. Hire for them that way on purpose, say so at the outset, and build the handover into the first week. People on a season contract who know what it is tend to give it their best. People who assume it is permanent and find out otherwise do not.
Borrow
Contractors and short engagements fall here, and the question is how fast a stranger can pick up the work and how cleanly they can hand it back. How long a newcomer takes to become useful is the best measure of your own process.
Fill in the buckets honestly
Write down every role you depend on and put it in a bucket. Put a name against each, and next to the name write your honest estimate of how long you expect them to stay. Most managers find that the Keep bucket is smaller than they had assumed, and that someone they thought of as permanent is closer to a season.
That is useful information. It changes what you say in a one-to-one, how you hire, and where you spend the budget.
Look at the market as well as the team
The same exercise applies outside your walls. Some roles have more available talent than you can interview. Others are scarce, and every offer you make competes with three more. If the roles in your Keep bucket are also the scarce ones, that is your highest risk, and it should be on someone's list.
Review twice a year
People move between buckets. A contractor becomes a colleague, and a long-serving engineer announces a move abroad and becomes a season. Twice a year is often enough to catch it, and a good moment is just after your planning cycle, when you are already looking at the year ahead.