You are NOT liable for debit fraud over $50 on your account, provided you notify the bank within 3 days of it occurring. The $50 exemption for banks is to incentivize you to report fraud quickly rather than waiting until the end of the statement cycle and looking at the paper, long after the fraudster has disappeared.
If your credit sucks too much to get a real credit card through a credit union---go get a secured credit card from people like Public Savings Bank or a credit union that offers secured credit cards. You put up a security deposit and that's your credit line. If you close the account, you get the deposit back. If you get the secured card through some banks like CapOne, etc---they may unsecure the card after a while and return your deposit, which means then you have an unsecured credit card with a credit line.
Nonetheless... good luck with some of these banks in getting NSF funds due to fraud reversed. Large banks generally do whatever they can to keep their fee income, including pissing you off to the point where you close your account and take all your business away. Large national and regional banks as a whole only get concerned if you're a large customer that has significant deposits; mostly because branch managers do get graded on retail stats like how many new accounts opened and products purchased, etc. Losing a big depositor makes weekly stats look ugly, so they will bend over to save you. They really don't care much about the depositor who can barely keep $1,000/£500 in the bank.
The same goes with lending products. Customers with excellent credit (which the banks checks periodically by doing soft pulls on the credit bureaus), revolve their accounts somewhat and generate lots of transaction volume are woo'd and if you call to cancel a card--you will get xfer'd to a "customer save" department... ALWAYS manned by native English speakers, where they try to save the account from closure. Contrast that with borrowers with mediocre credit, make only minimum payments, late-pay or don't use their accounts much at all, the bank is happy to see them go.
You should always use a credit card when making purchases because it's the bank's money on the line, not your own and if you detect fraud, you can ask for a chargeback. Chargebacks cause the merchant to get money wiped off their credit card remittances for the amount of the chargeback.
I did a chargeback once when a kid at Starbucks rang up my coffee, twice, on two tickets. I only got one receipt but when I checked my credit card statement... two transactions for the same money for the same day hit my account. I clicked on the charge and clicked "Contest charge" and explained why I thought it was wrong. The next day the charge was gone off my statement, and that Starbucks store got $4.96 wiped off their credit card remittances for charging me twice, which leaves it to their store manager to search their records to find out why they got a chargeback and who caused it to happen, etc.
You can't easily do chargebacks with debit cards because you have to fight your bank. With credit cards it's easy, because Visa/MC/Amex/DISC build purchase protection into their credit card contracts.