I sometimes use my dock, can I prevent it from being booked?

Definitely.  Each of your listings will have its own listing calendar that shows upcoming booked dates and also any private bookings you may have added.  From the same listing calendar page, you can block out additional dates where you will be using the listing or need it empty.

If your listing will not be available for long periods of time, you can also pause the listing completely which will prevent it from being shown in search results and also prevent bookings of any kind.