Line Symbol for Castles?

[hm_stella]

Hi folks, 

I am currently making a map for the city, and stuck in a problem

I have to change the line symbol for the Castle walls with the symbol like the below.

However, as soon as I change the line with this pic, it makes a weird result looks like this.

It seems like when the line is curving, the symbol can't follow it. Does anyone know how to fix this, or have a line symbol style (stylx) for this?

Thanks!