поставить или отдавать под залог!
"Поставить под залог" is incorrect.
"Отдать под залог" is to phisically give something away to someone as guarantee of loan. Someone will give it back after return of loan.
Use simple "заложить": "...я должен заложить небольшой участок земли или машину (которую куплю)."
P.S.
Ипотека is form of залог which is:
a) you get money to buy house
b) you live in it and use it from start
c) but if you fail with payments lender has right to sell it
d) after completing payments you will own it