I agree that there are situations when plants may need to be in pots. But it should not be done otherwise because you are removing a very important aspect of a healthy aquarium which begins in the substrate. The other day I posted this as a question because I was interested in the reasoning behind it. Not surprisingly, no one gave any scientific evidence beyond individual preferences. That's fine, but when one is considering an aspect of the aquarium where the biological system will be impacted one way or the other, factual evidence is of more importance than my own preference. Walstad cites a number of studies dealing with the oxygenation of the substrate from rooted plants, and concluded that "the evidence suggests that plant roots have a major impact on sediment ecology, stimulating the processing and recycling of sediment nutrients and toxins. Without the normal root-release of oxygen and organic compounds by aquatic plants, the substrate could become a mulm-ridden 'dead zone'." Sound familiar? Now to your questions here.
Once sword plants are established, most fish will not have any success uprooting them. I am talking smallish fish, not foot-long cichlids. I have used a sand bed of four inches in my 5-foot tank, down to 1.5 or 2 inches in smaller tanks. I push the roots down to the bottom glass, then pile the sand up around the plant. Then very gently pull the crown exactly vertically until it is exposed. Sometimes I have a chunk of wood next to the plant, this is very "natural" as plants often root next to such objects in nature. I sometimes use rounded river rocks.
I would not use metal weights, there may or may not be issues with the metal; it just isn't needed so I won't risk it.