Mobilization in the fence world means getting to your job site, delivering materials and setting up for the job.
Mobilization costs for small, local fence jobs is typically a short process and is usually built into the quote you get from your fence company.
On larger fence projects, however, most contractors will provide a separate rate for mobilization and possibly for demobilization too. This rate may be charged more than once if the contractor has to leave the site and then return at a later stage to finish the work - depending on the reason they demobilize.
Planning your projects carefully to minimize the number of times your fence contractor needs to leave the job and return later, and ensuring that the site and fence line is ready for the installation is the best way to keep mobilization costs low.