Correct

防线

/ fáng xiàn / 
Strokes

Definition

defensive line or perimeter/CL:道[dào]

Example

As a Noun

line of defence

1
Fángxiàn
防线
wěngù
稳固

have a strong defence

2
Tūpò
突破
fángxiàn
防线

break through the line of defence; get through/penetrate the guard