If your spouse wants to oppose your divorce and you have been separated for more than one year, then there is very little they can do to stop it. Once you have filed an application, they must file materials claiming that the two of you have actually not been living separate and apart for that period of time. If they choose to do this they may be able to delay your divorce, but in most cases you can fairly easily provide evidence of the truth and your divorce will go through. A brief attempt at reconciliation after your initial separation (less than 90 days) will not count towards interrupting the one year separation period.
One way your spouse can make things more difficult for you is if they actively attempt to avoid service of the divorce documents. If you think this might occur, you can simply avoid warning your spouse of your intentions and a process server can easily surprise them with the documents. Once the process server confirms a person’s identity, they can leave the documents with that person even if the person refuses to physically take them.
A more difficult situation occurs if you cannot find your spouse at all. In this situation you must prove to the court that you made significant efforts to find your spouse. This can include telling the court that you have spoken to family and friends, tried to contact your spouse via email and Facebook and taken any other obvious steps you could think of. You will have to fill out additional paperwork to prove this and you may want to retain a lawyer to help you do so to convince the court that you have done this thoroughly.