BE SURE of the soil , need a fairly strong foundation, also be aware of water logging, if water logs in your place please allow drainage holes (weep holes)
as water logging will be soaked up by the blocks here ( very very very poor standard)
i would advise both supervising and making the blocks your self, what most block makers sell is rubbish, and it will crumble before your eyes, also the wind will be a factor too, if it is a wind prohibitor, a good storm will make shiiit of it
my tuppence worth would be just to use some good barbed wire for now, get your self some real real thorny plants ( like blackthorn or whitethorn)
i got them bare root from ireland two years ago and they are all fine and healthy, and just three more years and the wind it self wont get through not to mind the nosy locals)
you can buy said trees as bare root (can be bought in winter season only as the tree is asleep) and transported no bother and just plant as saplings
these would be so much better than a hollow block wall, and natural as can be, have lovely flowers and these trees can be trained will grow in any soil and are stormproof, typhoon proof and fantastic sugnod that never needs drying