Is it permissible to leave work for Jumu'ah prayer, which my work prevents me from attending four times a month?

If guarding the company requires your presence at the time of the Friday prayer, then you are excused, and there is no sin upon you for missing the Friday prayer. You should pray Dhuhr. If you choose to leave this job to attend the Friday prayer, this is a good intention, and you will be rewarded for it, provided there is no greater harm in leaving it.