Harry is a relative newbie at ward-smithing. The ways around and through his wards are big enough for a herd of elephants to run through. Plus, he rarely puts enough effort into making his Wards that we see - not nearly as much as he puts into Little Chicago, for example. The point of Warding is to spend a long time into building a defense that takes an equal effort to penetrate. How this benefits you;
1) The enemy cannot penetrate the Ward -not powerful enough- and you're safe.
2) The enemy needs time to penetrate the ward - time you spend buffing up and/or preparing your big guns to flatten him when he does breach it.
3) An enemy has to spend his resources to breach the ward so when you do face him he is so much weaker while you are actually stronger for spending the time preparing.
For most master wizards, #1 applies against 99% of their enemies.
#2 means that even bigger fish take time to reach the wizard. If you spent a year raising the ward in your free time and the enemy is ten times as strong as you are, it will still take him a month to break through. Most baddies don't bother wasting a month against you, especially if at the end if the month, they take in the face a death-spell you spent the whole month casting.
#3 means that if the baddie is determined enough and spends enough resources, they do get to fight you - when they are at their weakest and you are at your strongest. If they were to win that fight, they'd win any other fight anyway. So better to make a last stand and try and take them with you or they're going to flatten you at any other battlefield.
As for compels, there are four types of people that make big Wards their main business;
1) Those whose job is to guard something important and that's their greatest goal in life. (i.e. Gatekeeper and the wards on the Outer Gates)
2) Those paranoid guys or people with large numbers of enemies who spend most their life in their magical fortress.
3) Old wizards that have retired from active duty or go to desk jobs, living under polar ice caps or distant planes and have nothing better to do.
4) Happy-go-lucky or insane people that build the Dark Tower of Ominousness because its awesome, big and cylindrical. And because they can.
#1 you can hardly compel away from their duty, especially if they're oathbound as well as have chosen that life.
#2 have been self-compelling themselves to stay inside their wards in the first place.
#3 don't much care if they're compelled. They've been building the Wards as an alternative to playing cards or gardening.
#4 want to be compelled out of their tower. They need the excuse to use their
other pet project after all; their army of undead, demons and outsiders. Yes, they might go down but there will be rain-o-fire and wailing and gnashing of teeth... which was their goal all along.
As you can see, those four types of people are not your typical PCs. But they could be if the game was epic enough.