To understand the problem posed by the ownership of land in a mix marriage couple you need to take in account a few different laws, but to make it short, the problm is here:
Law number 5 year 1960 in its article 21 says that only indonesian can own land
Law number 1 year 1974 in its article 35 says that everything buy a couple during the time of the marriage is joint property.
A prenup agreement is a good way to overcome the legal problems that could arise in case of divorce. It has to state, among other requirements, that the two future married are two separate parties. Ideally it should be done along with a last will and testament which would stipulate to whom (Indonesian citizen) the Hak Milik (property of the land) would revert in case of his/her death and that the surviving foreign husband/wife is entitled to a Hak Pakai which would become immediately in effect!
Legally, prenup agreement are recognise by Indonesian courts.
Problems could arise if there is no prenup nor will and that someone in the family contest the inheritance or the legal possession of the land.
Anyway getting married in Indonesia, or wherever in the world, has serious legal consequence. You have to seek the advice of an knowledgeable attorney. Not only a notaris who has no right or experience to argue a case in court.