Use condoms. Keep one or two in your wallet at all times. Also get hold of the morning after pill if at all possible, and keep it somewhere convenient like in your car. Then you have a backup option if the condom breaks. Mind you, I have never had a condom break. Australian condoms are made to a very high standard and should never break IMO (it's impossible to break them with your fingers deliberately, unlike some of the shit I have bought overseas which often breaks while I am trying to force it onto my wanger)... so if you are concerned, get some of those. And be sensible, no staying around -- after you cum, withdraw and dispose of the condom. In fact it is best to take the condom with you, since some women will steal your sperm and impregnate themselves with it. Also I suggest to get an STD check once per year, I recently discovered my GP can order these, so there is no need to go to a sexual health clinic or do anything out of your comfort zone.
Ray
+1 Smith, I had gotten extremely lazy (didn't use condoms every time with regular partners and also didn't use if having erection issues or I had lost them or a whole host of other reasons) and yes my gf insisted on not using condoms, result: one pregnancy and my having to tell 4 girls including my pregnant girlfriend that they might have chlamydia... fuckin hell, a huge mess that is now basically under control, but unnecessary had I made it a hard rule. MAKE IT A HARD RULE.