To 'protect' is to do something effective enough so that you will not have to 'defend'. The difference between the words matter in real life.
To 'defend' is when something is ALREADY under attack. It is reactive. This is when violence is the response to violence. At this point, it is either all or nothing. If you lose the fight, meaning your defenses failed, you lose that something.
To 'protect' is proactive and preemptive. You have to make it clear that something will be costly to whoever want it thru violent means. It is less costly to you, in the long run, to protect than to defend. By the time you have to defend -- fight -- you may lose more than just things but people. That is not what you want.
So how do the difference between the two words matter in real life ? The difference affects your policies, your finance, and your military posture.
An enemy do not attack unless he is confident that he WILL win. Not that he can win, but WILL win. It does not matter if he is overconfident or not. A judgement of being 'overconfident' is external, meaning that judgement is from observers. In the real fight, he may lose, but he would not know it until it is too late. Nevertheless, you cannot rely on hope but on what you can do.
You have to insert as much uncertainty as possible into everything he wants to do so that instead of being confident that he will win, he is confident that he can win. Anybody can do something. In theory, I can go to the Moon. If NASA done it, so can I. The difference is that NASA with all of its resources was confident that it will be successful, not merely can be successful.
The first item you need is sufficient resources to create that sense of uncertainty. That does not mean Viet Nam have to start a crash program of military modernization including aircraft carriers, heavy cruisers, etc. If Viet Nam have the money -- great. But financial constraints demands Viet Nam to be judicious with spending so the problem is what kind of resources should Viet Nam feasibly have in order to insert that sense of uncertainty into China's expansionist plans.
The second item you need is assessment of what can China deploy to the region to convince you, or create uncertainty into you, that you cannot resist China's moves. The latest assessment now is that China's air power is not as persistent as China's sea power. That mean any conflict, or implied conflict, in the SCS will be ship vs ship. China's air power is still sufficiently weak that it can be deterred by surface response, aka surface to air missiles (SAM). Not yet requiring direct air-air methods.
The third item you need is self assessment. What do you have at THIS time that you can use to insert that sense of uncertainty into China's thinking ? Viet Nam and the others in the region should get thru all of your heads that China is NOT interested in diplomacy regarding the SCS, of which directly affects everyone's EEZ and the Spratly Islands. If China gains control of the SCS, the Spratly Islands are gone no matter how the UN rules and all your EEZs will be violated at China's convenience. What does Viet Nam have at this time that you can use and if you do not have enough of it, can you get the same from others in an alliance ?
The reason China is going thru the diplomacy theater is that China is not yet militarily powerful enough to take the SCS by force. Uncertainty can be a two-way street and China is using that theater skillfully. Everyone likes to think everyone is rational in the sense that everyone want peaceful resolutions to disputes. But history have shown that the decision to act militarily is EQUALLY rational as the decision to resolve disputes thru diplomacy. For control of the SCS, the diplomacy theater acts are there to create hesitancy in all of you. China is not being/acting 'crazy' with her military alternative.
My opinion is that no one in the region is militarily powerful enough -- BY HIMSELF -- to either create uncertainty in China's plan or to finally fight (defend) against China's military. I have always advocated an alliance. Since the method of protection and defense will be the ship, all of your navies must band together to create that uncertainty for China. Remember, it is better to protect than to defend. That mean everyone must have increased naval presence, not just in their respective EEZs but beyond. Everyone must demonstrate to China that as a collective, you will not be intimidated. Geographically, China have a greater distance to cover and support her navy than others in the region to support theirs.
I told this forum yrs ago when I first came here that after JPN, China will be the next aggressor in Asia.
If you -- everyone -- do not defend the SCS, none of you will have any EEZs.