Dog getting out of yard?

I'm hoping some people can help me brainstorm. For the last couple of months, one of our dogs has been escaping nearly every time she goes outside. Here is some background:

-She's spayed

-She gets plenty of exercise

-Our backyard is "fun" for a dog. Plenty of toys and a digging pit.

-She loves being outside

-We have a chain link fence and we have staked it with huge yellow stakes.

-She has gotten these stakes up before. No idea how. She just pulls them up.

-She will not go to the bathroom on a leash

-She gets out immediately and if we're inside or outside. We always watch her, either from the door or the porch.

-She usually gets out and then immediately wants back in but can't figure out how. But sometimes she roams the neighborhood.

-We've had to retrieve her from the pound twice. Which means she's willing to get into strangers' cars. This scares me. She could get hit by a car or go home with the wrong kind of people.

I feel like there's something I'm forgetting, but I can't think of it. We currently don't have the funds for a new fence or professional trainer advice.

We do not want to re-home her. We love her very much and she's a perfect dog in every way but this.

Is there anything we're overlooking? Anything we could try? Any reason she's doing this?