Translation:There is a tall fence around that garden.
"az" and "a" are the same word that just appears in different forms (as in, say, French, where "le" must be "l'" in front of a vowel). So there is an "az" here, it's just spelled and pronounced as "a" ;-)
If you want to take it step by step, you might think of it something like taking "az a kert" ("that garden"), inserting "körul" at the required positions, giving "az körül a kert körül", and then changing the first "az" into an "a" because it's in front of a consonant. But I'm not sure that helps.
Aha; that makes perfect sense, thank you! For some reason it never occurred to me that the first 'az' in 'az a(z)' would change in the same way as the second...
So then, how would you say "There is a tall fence around the garden"? "A kert körul van egy magas kerítés"?
I think the repetition only occurs with 'this' and 'that', so:
around that garden: "a körul a kert körul" around this garden: "e körul a kert körul" around the garden: "a kert körul"
(Is that right?)
Replace Kert with Ország, and you get good, ol' Hungary, hehehe. (I know that the fence does not actually encirculate the country). Magyars keeping rapefugees out since 1456.