Security firm G4S has a good record of performing in tough times. In the last downturn, its top line growth never fell below 2%, and it has typically expanded at two percentage points above gross domestic product, notes James Ashton in the Sunday Times. Half-year results this week are expected to show 4% underlying sales growth ? not bad when some outsourcers are going backwards. That is made up from 8% growth in emerging markets and nearer 2% in mature ones like Britain. G4S shares are trading on 11 times this year's forecast earnings and nine times next year's. Analysts think it is capable of 4% growth for the full year, 6% in 2012 (helped by the Olympics) and 10% in 2013. Despite some short-term worries, the shares should be locked up.The recent market shake-out has thrown up some notable investment opportunities, claims Hargreaves Lansdown's Mark Dampler, in the Independent on Sunday. If you believe a full-blown recession will be avoided, oil exploration companies look very cheap and priced to reflect oil at $60 a barrel rather than the current value of around $100. Many small exploration and production companies have fallen 35 per cent to 70 per cent during the turmoil and an investment in Junior Oils Trust, a portfolio concentrating on profitable small producers, is a fund to consider, Dampler suggests."I am also a strong believer in gold and BlackRock's Gold & General Fund. In the short term physical gold looks a little overbought, but gold mining shares, like oil shares, look cheap relative to the physical commodity," Dampler adds. For investors seeking a defensive approach, absolute return funds could be used. Philip Gibb's Jupiter Absolute Return Fund has actually risen modestly during the crisis and remains a good diversifier for a portfolio. Troy Trojan, Miton Strategic Portfolio and Jupiter Strategic Bond could all be considered too, Dampler suggests. The market slump has not been kind to the Midas column's "Dogs of the Footsie" portfolio - the selection of shares that takes last year's worst performers and sees how well they bounce back this year. The companies in the portfolio- Aviva, AstraZeneca, BAE Systems, Man Group, National Grid, Resolution, RSA, Scottish & Southern Energy, Standard Life and Vodafone - have collectively slumped by 16% since May, a worse performance than the Footsie itself.Overall, the Dogs have had a disappointing summer but the average yield is now 7.3%, a genuine comfort in today's ultra-low interest rate environment, Midas in the Mail on Sunday assures.Gem Diamonds is worth holding on to, claims Questor in the Sunday Telegraph. The shares have fallen 28% since Questor last updated on Gem in May, but on Friday's interim results, they leapt by the most in nine months as its profits leapt tenfold to $79m from $7.8m last time. That means that they are currently trading at 11 times 2011 earnings, and are worth sticking with.Amec's chief executive Samir Brikho has done a good job since he took the reins five years ago, and is sitting on a pile of cash which he would prefer to invest in the business rather than return it shareholders, says James Ashton in the Sunday Times. JP Morgan Cazenove, Amec's broker, recently highlighted Clough, an Australian maker of oil equipment that it says would be a good fit. Whether Brikho has a deal up his sleeve or not, investors will be keen to hear his take on the current market turmoil when the company announces results this week. If there is a big slowdown coming, Amec, as the maker of kit and manager of projects for the big resources companies, will feel it sooner than most.Please note: Digital Look provides a round-up of news, tips and information that is impacting share prices and the market. Digital Look cannot take any responsibility for information provided by third parties. This is for your general information only as not intended to be relied upon by users in making an investment decision or any other decision. Please obtain a copy of the relevant publication and carry out your own research before considering acting on any of this information.