It is not desirable for a person to dig his grave ahead of time as this was not done by Prophet (peace be upon him) nor by his companions. A person does not know where he will die. If the intention of the person is to get ready for death, then preparation should be in good deeds. (See selections of Jurisprudence writings by Ibn Taymiyah, Funeral Rights, by al-Albani, p.160, 40th ed, Islamic Center).In otherwords, preperation for meeting Allaah, is not by digging graves. Instead, it is accomplished by overabundance of good deeds. If it is not possible in predominantly non-Muslim countries to have a cemetery or dedicated plot for the burial of Muslims unless the graves are reserved beforehand (e.g., to raise the funds), then there would be no objection in this case.