I have done law ones before.
Generally - ADR, Mediation, Intro to Bus Law and Tax Law (non law student) is offered each year.
From what lecturers have said, the others that are offered change year to year, sort of they take it in turns so to speak to do a summer unit.
Eg last year there was Human Rights Law, Immigration Law and some others.
Law students should have received a letter/email from Michael Adams some time ago which outlined the to be expected units available, so they seem to have these planned ahead of time.
If you want to know for law units, perhaps email the Law School and ask if there are any expected summer school units as yet
They may be able to give you some (unconfirmed) information.