Well, it is true that the more buds are dispersed on the plant, in terms of height, (i.e instead of one cola that's highest on the plant, multiple colas on equal height), each cola will be smaller (in weight and size), but they say that for some or most strains, the sum of all these colas will be larger than the single big cola. so you see what I'm saying.
alas, I do not have the experience to confirm or deny this theory, but it is quite acceptable in the growing world I believe, and this is why people scrog (in a scrog you have all the plant on an even, unified height canopy). I also don't know how this affects potency, but I would think it doesn't affect it much. Also, topping the plant for instance would get you the same results (multiple colas instead of one), and is good practice even if you do use LST or scrog. read some about these techniques.
as for a way to do it, well, just tying down the top would surely work. If you want maximum control on your plant, you can scrog it, but outdoor plants usually don't need such handling. I understand your main concern is security, and normally this is the first and ultimate priority when growing, all the rest comes afterwards. Keep in mind that with a very large plant you may need to work often on managing its height. If you tie its top down one day, you may find on the next that it just curled upwards from that point and continue to grow up, that's what plants do.
anyways, with plants of good genes growing in the ground with full on sunlight, assuming they are healthy, I don't think you should be concerned about yield or potency at all
so keep it secret, keep it safe! good luck
