Ⅰ.
keep a tight rein on sth
► to control something very carefully: »
We need to keep a tight rein on the advertising budget.
Main Entry: ↑rein
Ⅱ.
keep a tight rein on sth
► to control something, especially spending, in a very careful way: »
The chancellor was urged to keep a tight rein on public finances.
Main Entry: ↑tight
Financial and business terms. 2012.