No rack solution is totally secure. Usually I don’t think this a big problem and the risks are ones I am willing to take.
However, in your case it may be different The security issue in your case is that it sounds like you’re going to be leaving the bike on a rack in the same area often. That makes planning for a theft very easy. Along with already knowing exactly what tools they will need, they also know when the car is parked and for how long. Also, many racks with built and locks (such as with Yakima or Thule) the locks say right on them which key fits and anyone can order a new key.