Are unalienable rights really unalienable?

Recently in my English class we have been reading a book called Starship Troopers by Robert Heinlein. In this book the subject is brought up of whether or not the unalienable rights mentioned in the United States Declaration of Independence are really unalienable.
In the Declaration of Independence the founding fathers stated "...we hold these truths to be self evident that all men are created equal, that they are endowed by their creator with certain unalienable rights, that among these are Life, Liberty and the pursuit of Happiness..." Unalienable is a word defined as something that is not to be separated, given or taken away. But are these rights really unalienable no matter what the circumstance?
This same book also brings to focus the fact that freedom is not free, nor is anything worthwhile free. I believe this is true, partly because my own dad was in the military and I know for a fact that it is because of him and others that we have our freedom. Someone has to pay the price whether by hard work or by sacrificing their own life.
The founding fathers did not say, when they wrote this into the Declaration, that men are endowed with these unalienable rights as long as they work hard and obey the laws of society. However it is implied that this must occur because we do not live in a perfect world with perfect people. Therefore life, liberty and the pursuit of happiness must be sought after and worked for. Our founding fathers included this passage into the Declaration because they wanted Americans to at least have the opportunity to pursue each of these rights. In most countries people do not have these rights; take China for example. They are only allowed one child and the rest are just killed. Talk about taking away the right to life. As Americans we are lucky, we have the right and the privilege to pursuing happiness, life and liberty.
So are they really without question unalienable rights? Some could argue no. But I think yes, if you choose to work and put forth effort in pursuit of them.